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CBSE - Class 9 Mathematics Polynomials Worksheet
EXERCISE 2.4
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Solution:
We are tasked with evaluating the sum of three cubes without performing direct cubing operations. The given mathematical expression is:
$(-12)^3 + (7)^3 + (5)^3$
Let us define the base of each cubic term as a distinct variable:
Before attempting to expand the expression, we must analyze the linear sum of the base variables. This is a critical diagnostic step in polynomial algebra to determine if a conditional identity applies.
$a + b + c = (-12) + 7 + 5$
$a + b + c = -12 + 12 = 0$
[Geometrically, this represents a closed vector loop in one dimension, where the displacement from the origin returns exactly to zero. See the precise vector visualization below.]
We rely on the fundamental algebraic identity for the sum of three cubes:
$a^3 + b^3 + c^3 - 3abc = (a + b + c)(a^2 + b^2 + c^2 - ab - bc - ca)$
[Per the Zero Product Property], if the first factor on the right-hand side, $(a + b + c)$, is equal to zero, the entire right-hand side of the equation evaluates to zero, regardless of the values of the quadratic polynomial factor. Therefore:
$a^3 + b^3 + c^3 - 3abc = (0) \times (a^2 + b^2 + c^2 - ab - bc - ca)$
$a^3 + b^3 + c^3 - 3abc = 0$
Transposing $-3abc$ to the right side yields the conditional identity:
If $a + b + c = 0$, then $a^3 + b^3 + c^3 = 3abc$.
Since we have rigorously proven in Step 2 that $(-12) + 7 + 5 = 0$, we can directly substitute our variables into the conditional identity:
$(-12)^3 + (7)^3 + (5)^3 = 3 \cdot (-12) \cdot (7) \cdot (5)$
We now perform the sequential multiplication of the terms on the right-hand side:
To calculate $(-36) \times 35$ mentally or systematically:
$(-36) \times (30 + 5) = (-36 \times 30) + (-36 \times 5)$
$= -1080 - 180 = -1260$
Final Solution: The value of $(-12)^3 + (7)^3 + (5)^3$ is $-1260$.
Solution:
We are tasked with factorising the following multivariable polynomial of degree 2:
$P(x,y,z) = 2x^2 + y^2 + 8z^2 - 2\sqrt{2}xy + 4\sqrt{2}yz - 8xz$
The structure of this expression—comprising three squared terms and three cross-product terms—directly corresponds to the algebraic identity for the square of a trinomial. [Per the standard algebraic expansion theorem]:
$(a + b + c)^2 = a^2 + b^2 + c^2 + 2ab + 2bc + 2ca$
We begin by equating the pure squared terms from the given polynomial to the squared terms in the identity to find the absolute values of $a$, $b$, and $c$.
To assign the correct positive ($+$) or negative ($-$) signs to $a$, $b$, and $c$, we must analyze the signs of the cross-product terms in the given polynomial:
| Cross-Product Term | Given Value | Sign Analysis |
|---|---|---|
| $2ab$ | $-2\sqrt{2}xy$ | Negative. [Implies $a$ and $b$ have opposite signs]. |
| $2bc$ | $+4\sqrt{2}yz$ | Positive. [Implies $b$ and $c$ have the same sign]. |
| $2ca$ | $-8xz$ | Negative. [Implies $c$ and $a$ have opposite signs]. |
From the analysis above, $b$ and $c$ share the same sign, while $a$ has the opposite sign to both. We can conventionally set $b$ and $c$ as positive, which forces $a$ to be negative. Therefore, we define our terms as:
Note: Alternatively, setting $a$ as positive forces $b$ and $c$ to be negative. Both conventions are mathematically equivalent.
Before finalizing the factorization, we must rigorously verify that our chosen terms reconstruct the original polynomial exactly.
Since all terms perfectly align with the identity $(a + b + c)^2$, we substitute our derived values of $a$, $b$, and $c$ into the factored form.
$(a + b + c)^2 = (-\sqrt{2}x + y + 2\sqrt{2}z)^2$
To express this as a product of its factors, we write the squared binomial as the product of two identical trinomials.
Final Solution: The factorised form of the polynomial is $(-\sqrt{2}x + y + 2\sqrt{2}z)(-\sqrt{2}x + y + 2\sqrt{2}z)$.
(Note: Factoring out a $-1$ yields the equally valid alternative form: $(\sqrt{2}x - y - 2\sqrt{2}z)(\sqrt{2}x - y - 2\sqrt{2}z)$).
Solution:
We are tasked with expanding the following trinomial squared:
$(3a - 7b - c)^2$
To expand this expression systematically, we utilize the standard algebraic identity for the square of a trinomial [Derived from the distributive property of multiplication over addition]:
$(x + y + z)^2 = x^2 + y^2 + z^2 + 2xy + 2yz + 2zx$
We must map the terms of our specific expression to the variables in the standard identity. By rewriting the given expression as a sum, we ensure that the negative signs are correctly associated with their respective terms:
$(3a - 7b - c)^2 = (3a + (-7b) + (-c))^2$
By direct comparison with $(x + y + z)^2$, we establish the following variable assignments:
Substituting these mapped values into the expanded form of the identity yields:
$(3a + (-7b) + (-c))^2 = (3a)^2 + (-7b)^2 + (-c)^2 + 2(3a)(-7b) + 2(-7b)(-c) + 2(-c)(3a)$
We now evaluate each term individually, applying the rules of exponents [$(ab)^n = a^n b^n$] and the rules of sign multiplication:
Combining all the simplified terms from Step 3, we construct the final expanded polynomial:
$9a^2 + 49b^2 + c^2 - 42ab + 14bc - 6ca$
The algebraic identity $(x+y+z)^2$ can be visualized as the area of a square with side length $(x+y+z)$, partitioned into 9 distinct rectangular regions. The sum of the areas of these regions corresponds exactly to the terms in our expanded formula.
Final Solution: $9a^2 + 49b^2 + c^2 - 42ab + 14bc - 6ca$
Solution:
We are tasked with factorising the following algebraic expression:
$ 27p^3 - \frac{1}{216} - \frac{9}{2}p^2 + \frac{1}{4}p $
To systematically approach the factorisation, we first rearrange the terms in descending order of the powers of the variable $p$ [Per standard polynomial representation conventions]:
$ 27p^3 - \frac{9}{2}p^2 + \frac{1}{4}p - \frac{1}{216} $
The expression consists of four terms, beginning and ending with perfect cubes. This structural signature strongly indicates the expansion of the binomial cube identity. We recall the standard algebraic identity for the cube of a difference:
$ (a - b)^3 = a^3 - 3a^2b + 3ab^2 - b^3 $
We analyze the first and last terms of our rearranged polynomial to determine the values of $a$ and $b$.
To rigorously prove that the expression is indeed the expansion of $(3p - \frac{1}{6})^3$, we must substitute $a = 3p$ and $b = \frac{1}{6}$ into the middle terms of the identity ($-3a^2b$ and $+3ab^2$) and verify that they match the original polynomial.
Checking the second term ($-3a^2b$):
$ -3a^2b = -3(3p)^2\left(\frac{1}{6}\right) $
$ = -3(9p^2)\left(\frac{1}{6}\right) $
$ = -27p^2 \left(\frac{1}{6}\right) $
$ = -\frac{27}{6}p^2 $
Simplifying the fraction by dividing the numerator and denominator by 3:
$ = -\frac{9}{2}p^2 $
[This perfectly matches the second term of our rearranged polynomial.]
Checking the third term ($+3ab^2$):
$ +3ab^2 = 3(3p)\left(\frac{1}{6}\right)^2 $
$ = 9p\left(\frac{1}{36}\right) $
$ = \frac{9}{36}p $
Simplifying the fraction by dividing the numerator and denominator by 9:
$ = \frac{1}{4}p $
[This perfectly matches the third term of our rearranged polynomial.]
Since all four terms of the given polynomial perfectly map to the expansion of $(a - b)^3$, we can confidently compress the expression into its factorised binomial cube form.
Substituting $a = 3p$ and $b = \frac{1}{6}$ into $(a - b)^3$ yields:
$ \left(3p - \frac{1}{6}\right)^3 $
To express this as a complete factorisation (a product of irreducible polynomials), we write the binomial three times:
$ \left(3p - \frac{1}{6}\right) \left(3p - \frac{1}{6}\right) \left(3p - \frac{1}{6}\right) $
Final Solution: The fully factorised form of the given polynomial is $ \left(3p - \frac{1}{6}\right) \left(3p - \frac{1}{6}\right) \left(3p - \frac{1}{6}\right) $.
Solution:
To evaluate the product $104 \times 96$ without performing direct arithmetic multiplication, we must express both factors in terms of a common, easily computable base. Observing the numerical values, both $104$ and $96$ are symmetrically distributed around the base value of $100$.
Substituting these expressions back into the original product, we obtain:
$104 \times 96 = (100 + 4)(100 - 4)$
The formulated expression $(100 + 4)(100 - 4)$ perfectly matches the structure of a fundamental polynomial identity [Per the algebraic identity for the product of the sum and difference of two terms].
The standard identity is defined as:
$(a + b)(a - b) = a^2 - b^2$
By mapping our specific variables to the identity, we establish:
Applying the identity to our expression yields:
$(100 + 4)(100 - 4) = (100)^2 - (4)^2$
The algebraic identity $(a+b)(a-b) = a^2 - b^2$ can be rigorously proven through geometric area conservation. The area of a rectangle with dimensions $(a+b)$ and $(a-b)$ is mathematically equivalent to the area of a large square of side $a$ minus the area of a smaller square of side $b$.
We now compute the numerical values of the squared terms derived in Step 2:
Substitute these calculated values back into the difference equation:
$10000 - 16$
Performing the final subtraction operation:
$10000 - 16 = 9984$
Final Solution: 9984
Solution:
The volume of a cuboid is defined by the product of its three mutually perpendicular dimensions: length ($l$), width ($w$), and height ($h$).
Mathematically, this is expressed as:
$V = l \times w \times h$ [Per the geometric definition of a rectangular prism's volume]
We are given the volume of a cuboid as a polynomial expression in terms of variables $k$ and $y$:
$V(y) = 12ky^2 + 8ky - 20k$
To find the possible expressions for the dimensions, we must factorize this polynomial into three distinct linear factors, which will correspond to the length, width, and height.
We begin by analyzing the terms of the polynomial: $12ky^2$, $8ky$, and $-20k$. We look for the highest common numerical coefficient and the highest degree of common variables.
Factoring out the GCF ($4k$) from the entire expression yields:
$V(y) = 4k \left( \frac{12ky^2}{4k} + \frac{8ky}{4k} - \frac{20k}{4k} \right)$
$V(y) = 4k(3y^2 + 2y - 5)$
The expression inside the parentheses is a quadratic polynomial of the form $ay^2 + by + c$, where $a = 3$, $b = 2$, and $c = -5$. We will factorize this using the method of splitting the middle term.
We must find two numbers that satisfy two conditions simultaneously:
The factors of $-15$ that add up to $2$ are $5$ and $-3$. We rewrite the middle term ($2y$) using these two numbers:
$3y^2 + 5y - 3y - 5$
Next, we group the terms into pairs to factor by grouping:
$(3y^2 - 3y) + (5y - 5)$
Factor out the common terms from each binomial group:
$3y(y - 1) + 5(y - 1)$
Since $(y - 1)$ is a common binomial factor, we can factor it out:
$(3y + 5)(y - 1)$
Substituting the factorized quadratic back into our volume equation, we get the completely factorized form of the volume:
$V = 4k \cdot (3y + 5) \cdot (y - 1)$
Because the volume of a cuboid is the product of three dimensions ($l \times w \times h$), these three factors represent the possible expressions for the length, width, and height of the cuboid.
Below is a precise oblique projection of the cuboid, illustrating how the three algebraic factors map to the spatial dimensions.
Final Solution: The possible expressions for the dimensions of the cuboid are $4k$, $(3y + 5)$, and $(y - 1)$.
Solution:
We are tasked with evaluating the numerical expression $(99)^3$ without relying on direct, brute-force multiplication. To achieve this with mathematical rigor, we must utilize standard algebraic identities.
To apply an algebraic identity, we must first express the base number, $99$, as a binomial. The most computationally efficient approach is to express $99$ as the difference between a power of $10$ and an integer, as powers of $10$ are trivial to exponentiate.
$99 = 100 - 1$
Therefore, the expression becomes:
$(99)^3 = (100 - 1)^3$
The expression $(100 - 1)^3$ perfectly matches the standard binomial expansion identity for the cube of a difference [Per the Binomial Theorem for $(a-b)^n$ where $n=3$]. The identity is defined as:
$(a - b)^3 = a^3 - 3a^2b + 3ab^2 - b^3$
Note: This is the expanded form of $(a - b)^3 = a^3 - b^3 - 3ab(a - b)$, which allows for clear, term-by-term evaluation.
By mapping our binomial to the identity, we establish the following variable assignments:
Substituting these specific values into the expanded identity yields:
$(100 - 1)^3 = (100)^3 - 3(100)^2(1) + 3(100)(1)^2 - (1)^3$
We now compute each of the four terms individually to ensure absolute arithmetic precision.
| Algebraic Term | Substitution | Calculated Value |
|---|---|---|
| $a^3$ | $(100)^3$ | $1,000,000$ |
| $-3a^2b$ | $-3(100)^2(1)$ | $-30,000$ |
| $+3ab^2$ | $+3(100)(1)^2$ | $+300$ |
| $-b^3$ | $-(1)^3$ | $-1$ |
The following flowchart maps the distribution of the binomial cube into its constituent polynomial terms before final synthesis.
Substituting the evaluated terms back into the expanded equation, we perform the final addition and subtraction sequentially from left to right:
$(99)^3 = 1,000,000 - 30,000 + 300 - 1$
First, subtract $30,000$ from $1,000,000$:
$1,000,000 - 30,000 = 970,000$
Next, add $300$:
$970,000 + 300 = 970,300$
Finally, subtract $1$:
$970,300 - 1 = 970,299$
Final Solution: $(99)^3 = 970,299$
Solution:
We are tasked with factorising the following algebraic expression:
$64m^3 - 343n^3$
Upon initial inspection, the expression consists of two terms separated by a minus sign. The variables $m$ and $n$ are both raised to the third power, which strongly indicates that we must evaluate the numerical coefficients to determine if they are also perfect cubes.
To apply the relevant algebraic identity, we must rewrite both terms entirely as perfect cubes in the form of $x^3$ and $y^3$.
Substituting these back into the original expression yields:
$(4m)^3 - (7n)^3$
The expression is now explicitly in the form of a difference of two cubes. [Per the fundamental algebraic identities of polynomials], the difference of two cubes is factored using the following formula:
$x^3 - y^3 = (x - y)(x^2 + xy + y^2)$
By mapping our specific terms to the identity, we establish the following equivalencies:
We now substitute these values directly into the right-hand side of the identity, $(x - y)(x^2 + xy + y^2)$:
$= (4m - 7n) \left[ (4m)^2 + (4m)(7n) + (7n)^2 \right]$
To achieve the final factorised form, we must expand the terms within the square brackets by applying the exponent rules [specifically $(ab)^n = a^n b^n$] and performing basic multiplication:
Substituting these simplified components back into our factored expression yields:
$= (4m - 7n)(16m^2 + 28mn + 49n^2)$
Final Solution: $(4m - 7n)(16m^2 + 28mn + 49n^2)$
Solution:
We are tasked with expanding the following trinomial squared:
$(–2x + 3y + 2z)^2$
To expand this expression systematically, we utilize the standard algebraic identity for the square of a trinomial [Derived from the distributive property of multiplication over addition]:
$(a + b + c)^2 = a^2 + b^2 + c^2 + 2ab + 2bc + 2ca$
By comparing the given expression $(–2x + 3y + 2z)^2$ with the standard identity $(a + b + c)^2$, we establish the following one-to-one correspondence for the terms:
Note: It is critical to include the negative sign in the assignment of $a$ to ensure the cross-terms are calculated with the correct parity.
Substituting the mapped variables into the expanded form of the identity yields:
$(-2x + 3y + 2z)^2 = (-2x)^2 + (3y)^2 + (2z)^2 + 2(-2x)(3y) + 2(3y)(2z) + 2(2z)(-2x)$
We now evaluate each term individually, applying the rules of exponents [$(xy)^n = x^n y^n$] and the rules of signed multiplication:
| Component | Calculation | Result |
|---|---|---|
| $a^2$ | $(-2x) \cdot (-2x)$ | $4x^2$ |
| $b^2$ | $(3y) \cdot (3y)$ | $9y^2$ |
| $c^2$ | $(2z) \cdot (2z)$ | $4z^2$ |
| $2ab$ | $2 \cdot (-2x) \cdot (3y)$ | $-12xy$ |
| $2bc$ | $2 \cdot (3y) \cdot (2z)$ | $12yz$ |
| $2ca$ | $2 \cdot (2z) \cdot (-2x)$ | $-8zx$ |
Combining all the simplified terms from Step 3 into a single polynomial expression:
$4x^2 + 9y^2 + 4z^2 - 12xy + 12yz - 8zx$
The algebraic identity $(a+b+c)^2$ can be geometrically proven by calculating the area of a square with side length $(a+b+c)$. The total area is the sum of the 9 smaller rectangular regions, which perfectly mirrors our algebraic expansion.
Final Solution: The expanded form of $(-2x + 3y + 2z)^2$ is $4x^2 + 9y^2 + 4z^2 - 12xy + 12yz - 8zx$.
Solution:
We are tasked with factorising the following binomial expression:
$27y^3 + 125z^3$
To factorise this polynomial, we must first analyze the coefficients and the degrees of the variables to identify any underlying algebraic structures. We observe that both terms are perfect cubes.
We determine the cube roots of the numerical coefficients and the variables:
Rewriting the original expression, we get:
$(3y)^3 + (5z)^3$
The expression is now explicitly in the form of the sum of two cubes, $a^3 + b^3$. [Per the fundamental algebraic identity for the sum of cubes, derived from the expansion of $(a+b)^3 - 3ab(a+b)$], we know that:
$a^3 + b^3 = (a + b)(a^2 - ab + b^2)$
By mapping our terms to the identity, we set $a = 3y$ and $b = 5z$. Substituting these into the right-hand side of the identity yields:
$(3y)^3 + (5z)^3 = (3y + 5z) \left[ (3y)^2 - (3y)(5z) + (5z)^2 \right]$
We must now rigorously simplify each term inside the second set of parentheses (the quadratic trinomial factor):
Replacing the unsimplified terms in our expanded equation with these calculated values, we obtain the final factorised expression:
$(3y + 5z)(9y^2 - 15yz + 25z^2)$
Final Solution: The completely factorised form of $27y^3 + 125z^3$ is $(3y + 5z)(9y^2 - 15yz + 25z^2)$.
Solution:
We are given the following polynomial expression of degree 3:
$P(a,b) = 64a^3 - 27b^3 - 144a^2b + 108ab^2$
To facilitate the identification of standard algebraic structures, we rearrange the terms in descending order of the powers of the first variable, $a$, and ascending order of the powers of the second variable, $b$.
$P(a,b) = 64a^3 - 144a^2b + 108ab^2 - 27b^3$
The rearranged polynomial consists of four terms, with alternating signs ($+, -, +, -$), and the first and last terms appear to be perfect cubes. This structural signature strongly indicates the application of the standard binomial expansion identity for the cube of a difference [Per the Binomial Theorem for $(x-y)^n$ where $n=3$]:
$(x - y)^3 = x^3 - 3x^2y + 3xy^2 - y^3$
We equate the first and last terms of our polynomial to the corresponding terms in the identity to find the base variables $x$ and $y$.
To rigorously prove that the polynomial is indeed a perfect cube, we must verify that the middle terms of the given expression exactly match the $-3x^2y$ and $+3xy^2$ terms of the identity when $x = 4a$ and $y = 3b$.
Since all four terms map perfectly to the $(x - y)^3$ identity, we can rewrite the entire polynomial in its unexpanded structural form.
$64a^3 - 144a^2b + 108ab^2 - 27b^3 = (4a)^3 - 3(4a)^2(3b) + 3(4a)(3b)^2 - (3b)^3$
By applying the identity $(x - y)^3$, we condense the expression into a single perfect cube:
$P(a,b) = (4a - 3b)^3$
To express this as a product of irreducible linear factors (which is the standard convention for complete factorization), we expand the exponent:
$P(a,b) = (4a - 3b)(4a - 3b)(4a - 3b)$
Final Solution: The completely factorised form of the polynomial $64a^3 - 27b^3 - 144a^2b + 108ab^2$ is $(4a - 3b)(4a - 3b)(4a - 3b)$.
Solution:
We are tasked with factorising the following algebraic expression:
$8a^3 + b^3 + 12a^2b + 6ab^2$
By analyzing the structure of the polynomial, we observe that it contains four terms, all of which are positive. Furthermore, the first and second terms ($8a^3$ and $b^3$) are perfect cubes. This structural signature strongly indicates the application of the standard binomial expansion identity for the cube of a sum [Per the Binomial Theorem for exponent 3].
The standard identity is defined as:
$(x + y)^3 = x^3 + y^3 + 3x^2y + 3xy^2$
Our objective is to map the given polynomial to the right-hand side of this identity.
We must rewrite the perfect cube terms to identify the base variables $x$ and $y$.
To rigorously prove that the identity applies, we must verify that the remaining terms in the polynomial ($12a^2b$ and $6ab^2$) perfectly match the $3x^2y$ and $3xy^2$ components of the identity using our established $x = 2a$ and $y = b$.
The following diagram illustrates the exact one-to-one mapping between the standard identity and our decomposed polynomial.
Since all terms perfectly satisfy the expansion of $(x + y)^3$, we can condense the expanded polynomial into its factorised binomial cube form by substituting $x = 2a$ and $y = b$:
$(2a)^3 + (b)^3 + 3(2a)^2(b) + 3(2a)(b)^2 = (2a + b)^3$
To express the polynomial fully factorised into irreducible linear polynomials, we expand the exponent. [By the fundamental definition of exponents, $z^3 = z \cdot z \cdot z$].
$(2a + b)^3 = (2a + b)(2a + b)(2a + b)$
Final Solution: The completely factorised form of the polynomial $8a^3 + b^3 + 12a^2b + 6ab^2$ is $(2a + b)(2a + b)(2a + b)$.
Solution:
The area of a rectangle is geometrically defined as the product of its two adjacent spatial dimensions: length ($l$) and breadth ($b$). This relationship is expressed by the formula:
$\text{Area} = l \times b$
We are given the area of the rectangle in the form of a quadratic polynomial in terms of the variable $a$:
$\text{Area} = 25a^2 - 35a + 12$
[Per the Fundamental Theorem of Algebra and polynomial factorization principles], to find the possible expressions for the length and breadth, we must factorize this quadratic polynomial into the product of two linear binomials. These two resulting factors will represent the possible dimensions of the rectangle.
We will factorize the quadratic polynomial $P(a) = 25a^2 - 35a + 12$ using the method of splitting the middle term. We compare the given polynomial to the standard quadratic form $Ax^2 + Bx + C$ to identify the coefficients:
To split the middle term, we must find two real numbers, let us call them $p$ and $q$, that satisfy two specific conditions simultaneously:
Because the product ($300$) is positive and the sum ($-35$) is negative, [by the rules of integer arithmetic], both numbers $p$ and $q$ must be negative.
Let us evaluate the factor pairs of $300$ to find the correct combination:
| Factor Pair ($p, q$) | Product ($p \times q$) | Sum ($p + q$) |
|---|---|---|
| $-10, -30$ | $300$ | $-40$ |
| $-12, -25$ | $300$ | $-37$ |
| $-15, -20$ | $300$ | $-35$ |
The numbers $-15$ and $-20$ satisfy both conditions perfectly. Therefore, we will split the middle term $-35a$ into $-20a$ and $-15a$.
We substitute the split terms back into the original polynomial:
$P(a) = 25a^2 - 20a - 15a + 12$
Next, we group the terms into pairs to extract the greatest common monomial from each group:
$P(a) = (25a^2 - 20a) - (15a - 12)$
Factor out the greatest common divisor (GCD) from the first group ($5a$) and the second group ($3$):
$P(a) = 5a(5a - 4) - 3(5a - 4)$
Notice that the binomial $(5a - 4)$ is now a common factor in both terms. We factor out $(5a - 4)$ [by the Distributive Property of Multiplication over Addition]:
$P(a) = (5a - 4)(5a - 3)$
The factorization proves that a rectangle with an area of $25a^2 - 35a + 12$ can be constructed with sides measuring $(5a - 4)$ and $(5a - 3)$. Below is the geometric representation of this relationship.
Because multiplication is commutative ($l \times b = b \times l$), either of the two binomial factors can represent the length, and the remaining factor will represent the breadth.
Final Solution: The possible expressions for the length and breadth of the rectangle are $(5a - 3)$ and $(5a - 4)$.
Solution:
We are tasked with expanding the algebraic expression $(x + 2y + 4z)^2$. To execute this expansion systematically, we utilize the standard algebraic identity for the square of a trinomial.
[Per the distributive property of multiplication over addition, the square of a trinomial is given by the identity:]
$(a + b + c)^2 = a^2 + b^2 + c^2 + 2ab + 2bc + 2ca$
By comparing our given expression $(x + 2y + 4z)^2$ with the standard identity $(a + b + c)^2$, we establish a direct one-to-one mapping of the terms:
The algebraic expansion of $(a + b + c)^2$ can be geometrically interpreted as the area of a square with side length $(a + b + c)$, partitioned into nine distinct rectangular and square regions. The sum of the areas of these nine regions perfectly mirrors the terms in our algebraic identity.
Substituting the mapped variables into the right-hand side of the identity, we obtain the unsimplified expanded form:
$(x + 2y + 4z)^2 = (x)^2 + (2y)^2 + (4z)^2 + 2(x)(2y) + 2(2y)(4z) + 2(4z)(x)$
We now apply the laws of exponents [specifically $(xy)^n = x^n y^n$] and basic arithmetic multiplication to simplify each term independently.
| Term Category | Unsimplified Term | Algebraic Operation | Simplified Result |
|---|---|---|---|
| Square of First Term | $(x)^2$ | $x \cdot x$ | $x^2$ |
| Square of Second Term | $(2y)^2$ | $2^2 \cdot y^2$ | $4y^2$ |
| Square of Third Term | $(4z)^2$ | $4^2 \cdot z^2$ | $16z^2$ |
| First Cross-Product | $2(x)(2y)$ | $(2 \cdot 2) \cdot (x \cdot y)$ | $4xy$ |
| Second Cross-Product | $2(2y)(4z)$ | $(2 \cdot 2 \cdot 4) \cdot (y \cdot z)$ | $16yz$ |
| Third Cross-Product | $2(4z)(x)$ | $(2 \cdot 4) \cdot (z \cdot x)$ | $8zx$ |
Combining all the simplified terms from Step 3 yields the fully expanded polynomial. By convention, we write the squared terms first, followed by the cross-product terms in cyclical order ($xy$, $yz$, $zx$).
$(x + 2y + 4z)^2 = x^2 + 4y^2 + 16z^2 + 4xy + 16yz + 8zx$
Final Solution: The expanded form of $(x + 2y + 4z)^2$ is $x^2 + 4y^2 + 16z^2 + 4xy + 16yz + 8zx$.
Solution:
To evaluate the expression $(998)^3$ without performing direct, cumbersome multiplication, we utilize the fundamental algebraic identities derived from the Binomial Theorem. The objective is to express the base number, $998$, as a binomial $(a - b)$ where $a$ and $b$ are integers that are computationally simple to raise to higher powers.
We can rewrite the base as:
$998 = 1000 - 2$
Thus, the expression becomes:
$(998)^3 = (1000 - 2)^3$
We apply the standard algebraic identity for the cube of a binomial difference [Per the Binomial Expansion for $n=3$]:
$(a - b)^3 = a^3 - 3a^2b + 3ab^2 - b^3$
By mapping our specific values to the identity, we establish:
Substituting $a = 1000$ and $b = 2$ into the identity yields:
$(1000 - 2)^3 = (1000)^3 - 3(1000)^2(2) + 3(1000)(2)^2 - (2)^3$
We systematically evaluate each term in the expanded polynomial:
Now, we substitute the evaluated terms back into the expanded equation and perform the arithmetic operations sequentially to ensure precision:
$(998)^3 = 1,000,000,000 - 6,000,000 + 12,000 - 8$
Operation 1: Subtraction
$1,000,000,000 - 6,000,000 = 994,000,000$
Operation 2: Addition
$994,000,000 + 12,000 = 994,012,000$
Operation 3: Final Subtraction
$994,012,000 - 8 = 994,011,992$
Final Solution: $(998)^3 = 994,011,992$
Solution:
To expand the given expression $(\frac{3}{2}x + 1)^3$, we utilize the standard algebraic identity for the cube of a binomial. The expansion of a binomial sum cubed is derived from multiplying the binomial by itself three times: $(a+b)(a+b)(a+b)$.
The standard identity is defined as:
$ (a + b)^3 = a^3 + 3a^2b + 3ab^2 + b^3 $
[Theoretical Justification: By the Binomial Theorem for $n=3$, the coefficients follow the sequence 1, 3, 3, 1 from Pascal's Triangle, representing the geometric decomposition of a cube into one $a^3$ volume, three $a^2b$ volumes, three $ab^2$ volumes, and one $b^3$ volume.]
By comparing the given expression $(\frac{3}{2}x + 1)^3$ with the standard identity $(a + b)^3$, we establish the following variable assignments:
We will now substitute $a$ and $b$ into the identity and rigorously evaluate each of the four terms.
1. First Term ($a^3$):
$ a^3 = \left(\frac{3}{2}x\right)^3 $
$ a^3 = \frac{3^3}{2^3} \cdot x^3 = \frac{27}{8}x^3 $
[Applying the power of a product and quotient rules: $(\frac{p}{q} \cdot x)^n = \frac{p^n}{q^n} \cdot x^n$]
2. Second Term ($3a^2b$):
$ 3a^2b = 3 \cdot \left(\frac{3}{2}x\right)^2 \cdot (1) $
$ 3a^2b = 3 \cdot \left(\frac{9}{4}x^2\right) \cdot 1 $
$ 3a^2b = \frac{27}{4}x^2 $
3. Third Term ($3ab^2$):
$ 3ab^2 = 3 \cdot \left(\frac{3}{2}x\right) \cdot (1)^2 $
$ 3ab^2 = 3 \cdot \left(\frac{3}{2}x\right) \cdot 1 $
$ 3ab^2 = \frac{9}{2}x $
4. Fourth Term ($b^3$):
$ b^3 = (1)^3 = 1 $
Combine the evaluated terms to form the expanded polynomial. It is standard mathematical convention to write polynomials in descending order of their degree (from the highest power of $x$ to the constant term).
$ \left(\frac{3}{2}x + 1\right)^3 = \frac{27}{8}x^3 + \frac{27}{4}x^2 + \frac{9}{2}x + 1 $
Final Solution: The expanded form of the cube is $\frac{27}{8}x^3 + \frac{27}{4}x^2 + \frac{9}{2}x + 1$.
Solution:
We are tasked with expanding the following algebraic expression:
$(2x - y + z)^2$
To expand a trinomial squared, we utilize the standard algebraic identity for the square of a trinomial [derived via the distributive property of multiplication over addition]:
$(a + b + c)^2 = a^2 + b^2 + c^2 + 2ab + 2bc + 2ca$
By comparing the given expression $(2x - y + z)^2$ with the standard identity $(a + b + c)^2$, we establish a direct mapping of the terms. It is critical to include the negative sign in the mapping to maintain algebraic equivalence.
Substitute the mapped variables into the expanded form of the identity. We will compute the squared terms and the cross-product terms systematically.
1. Computing the Squared Terms ($a^2, b^2, c^2$):
2. Computing the Cross-Product Terms ($2ab, 2bc, 2ca$):
Now, we assemble all the computed components back into the framework of the identity:
$(2x - y + z)^2 = (4x^2) + (y^2) + (z^2) + (-4xy) + (-2yz) + (4zx)$
Simplifying the signs yields the final expanded polynomial:
$(2x - y + z)^2 = 4x^2 + y^2 + z^2 - 4xy - 2yz + 4zx$
The algebraic identity $(a+b+c)^2$ can be visualized geometrically as the area of a square with side length $(a+b+c)$. The total area is the sum of the areas of the 9 smaller rectangular regions formed by partitioning the sides into segments of lengths $a$, $b$, and $c$.
As demonstrated in the area model, the total area consists of one $a^2$, one $b^2$, one $c^2$, two $ab$ rectangles, two $bc$ rectangles, and two $ac$ rectangles, perfectly mirroring our algebraic expansion.
Final Solution: The expanded form of $(2x - y + z)^2$ is $4x^2 + y^2 + z^2 - 4xy - 2yz + 4zx$.
Solution:
The geometric area of a rectangle is defined by the product of its two adjacent spatial dimensions, length and breadth. Mathematically, this is expressed as:
[$Area = Length \times Breadth$]
We are given the area of a rectangle as a quadratic polynomial in terms of the variable $y$:
$Area = 35y^2 + 13y - 12$
To find the possible expressions for the length and breadth, we must factorize this quadratic polynomial into the product of two linear binomials. Each resulting binomial will represent one of the dimensions of the rectangle.
We will factorize the quadratic polynomial $ay^2 + by + c$ using the method of splitting the middle term. First, we identify the coefficients:
According to the product-sum factorization theorem, we must find two real numbers, let's call them $p$ and $q$, such that:
1. Their product equals $a \times c$:
$p \times q = 35 \times (-12) = -420$
2. Their sum equals $b$:
$p + q = 13$
To systematically find the values of $p$ and $q$, we analyze the prime factorization of the absolute value of the product ($420$):
$420 = 2 \times 210 = 2^2 \times 105 = 2^2 \times 3 \times 35 = 2^2 \times 3 \times 5 \times 7$
We need to group these prime factors into two numbers whose difference is $13$ (since the product is negative, one number must be positive and the other negative). Let us test combinations:
Since the sum must be positive ($+13$), the larger number must be positive. Therefore, our two numbers are $28$ and $-15$.
[$28 \times (-15) = -420$ and $28 + (-15) = 13$]
We substitute the middle term $13y$ with $28y - 15y$ in the original polynomial:
$35y^2 + 28y - 15y - 12$
Next, we apply factorization by grouping. We group the first two terms and the last two terms:
$(35y^2 + 28y) - (15y + 12)$
Extract the greatest common divisor (GCD) from each group:
For $(35y^2 + 28y)$, the GCD is $7y$:
$7y(5y + 4)$
For $-(15y + 12)$, the GCD is $-3$:
$-3(5y + 4)$
Now, substitute these back into the expression:
$7y(5y + 4) - 3(5y + 4)$
Notice that the binomial $(5y + 4)$ is a common factor. Factoring it out yields the final product of two linear expressions:
$(7y - 3)(5y + 4)$
Because multiplication is commutative [by the Commutative Property of Multiplication, $A \times B = B \times A$], either of these binomial factors can represent the length, and the other will represent the breadth.
Final Solution: The possible expressions for the dimensions of the rectangle are Length = $(7y - 3)$ and Breadth = $(5y + 4)$, or vice versa.
Solution:
We are tasked with finding the product of the following binomials:
$(x + 8)(x - 10)$
[Per the fundamental principles of polynomial multiplication], we can expand this expression using a standard algebraic identity rather than manual term-by-term distribution. This ensures computational efficiency and minimizes arithmetic errors.
The given expression is of the form $(x + a)(x + b)$. The corresponding standard algebraic identity is defined as:
$(x + a)(x + b) = x^2 + (a + b)x + ab$
By comparing the given expression $(x + 8)(x - 10)$ with the standard form $(x + a)(x + b)$, we establish the following exact parameter mappings:
Substituting the mapped values of $a$ and $b$ into the algebraic identity yields:
$(x + 8)(x - 10) = x^2 + (8 + (-10))x + (8)(-10)$
Next, we simplify the coefficients [By applying the axioms of integer addition and multiplication]:
Substituting these simplified values back into the expanded equation gives the final quadratic polynomial:
$x^2 - 2x - 80$
The following geometric area model illustrates the partial products of the binomial multiplication. [Note: While geometric lengths cannot physically be negative, the area model serves as a rigorous algebraic abstraction used to visualize the distributive property].
Summing the partial products from the area model confirms our algebraic derivation: $x^2 + 8x - 10x - 80 = x^2 - 2x - 80$.
Final Solution: $x^2 - 2x - 80$
Solution:
We are given the volume of a cuboid expressed as a polynomial in terms of a variable $x$:
$V(x) = 3x^2 - 12x$
[Per the geometric definition of a cuboid], the volume $V$ is the product of its three mutually perpendicular spatial dimensions: Length ($L$), Width ($W$), and Height ($H$). Mathematically, this is expressed as:
$V = L \times W \times H$
To find the possible expressions for the dimensions of the cuboid, we must factorize the given binomial polynomial into three distinct linear or constant factors.
We begin by analyzing the terms of the polynomial $3x^2 - 12x$ to extract the Greatest Common Factor (GCF). We decompose each term into its prime numerical and algebraic factors.
| Polynomial Term | Prime Factorization |
|---|---|
| $3x^2$ | $3 \cdot x \cdot x$ |
| $-12x$ | $-1 \cdot 2 \cdot 2 \cdot 3 \cdot x$ |
By comparing the factorizations, we identify the common elements:
Therefore, the overall Greatest Common Factor is $3x$.
[By the Distributive Property of Multiplication over Addition], we can factor out the GCF from the original expression:
$V(x) = 3x^2 - 12x$
$V(x) = 3x(x) - 3x(4)$
$V(x) = 3x(x - 4)$
We have now successfully expressed the binomial as a product of its irreducible factors.
The factored form of the volume is $3 \cdot x \cdot (x - 4)$. Because the volume of a cuboid requires three dimensions ($L \times W \times H$), we can directly map these three distinct factors to the dimensions of the cuboid.
Note: Because multiplication is commutative ($A \times B \times C = B \times C \times A$), any of these expressions can represent the length, width, or height.
Below is a high-precision spatial representation of the cuboid with its corresponding dimensional expressions.
Final Solution: The possible expressions for the dimensions of the cuboid are $3$, $x$, and $(x - 4)$.