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CBSE - Class 10 Mathematics Quadratic Equations Worksheet
EXERCISE 4.1
Worksheet Answers
Solution:
Given: The algebraic equation $(x - 2)(x + 1) = (x - 1)(x + 3)$.
To Find: Determine whether the given equation is a quadratic equation.
Definition: A quadratic equation in the variable $x$ is an equation of the form $ax^2 + bx + c = 0$, where $a, b, c$ are real numbers and $a \neq 0$.
Step 1: Expanding the Left-Hand Side (LHS)
The LHS is $(x - 2)(x + 1)$. We apply the distributive property of multiplication over addition: $(a + b)(c + d) = ac + ad + bc + bd$.
$(x - 2)(x + 1) = x(x) + x(1) - 2(x) - 2(1)$
$= x^2 + x - 2x - 2$
$= x^2 - x - 2$
Step 2: Expanding the Right-Hand Side (RHS)
The RHS is $(x - 1)(x + 3)$. Similarly, applying the distributive property:
$(x - 1)(x + 3) = x(x) + x(3) - 1(x) - 1(3)$
$= x^2 + 3x - x - 3$
$= x^2 + 2x - 3$
Step 3: Equating LHS and RHS and Simplifying
Now, set the expanded LHS equal to the expanded RHS:
$x^2 - x - 2 = x^2 + 2x - 3$
To bring all terms to one side, subtract $(x^2 + 2x - 3)$ from both sides:
$x^2 - x^2 - x - 2x - 2 + 3 = 0$
Combine like terms:
$(1 - 1)x^2 + (-1 - 2)x + (-2 + 3) = 0$
$0x^2 - 3x + 1 = 0$
$-3x + 1 = 0$
Step 4: Conclusion
The resulting equation is $-3x + 1 = 0$. This is a linear equation, not a quadratic equation, because the coefficient of $x^2$ is $0$ (i.e., $a = 0$). Since the definition of a quadratic equation requires $a \neq 0$, this equation does not satisfy the condition.
Final Answer: The given equation $(x - 2)(x + 1) = (x - 1)(x + 3)$ is not a quadratic equation.
Solution:
Given: The equation $(x^3 - 4x^2 - x + 1) = (x - 2)^3$.
To Find: Determine whether the given equation is a quadratic equation.
Step 1: Understanding the definition of a Quadratic Equation
A quadratic equation is an equation of the form $ax^2 + bx + c = 0$, where $a, b, c$ are real numbers and $a \neq 0$. The highest power (degree) of the variable $x$ must be exactly 2.
Step 2: Expanding the right-hand side (RHS)
The RHS is $(x - 2)^3$. We use the algebraic identity for the cube of a binomial:
$(a - b)^3 = a^3 - 3a^2b + 3ab^2 - b^3$
Here, $a = x$ and $b = 2$.
$(x - 2)^3 = x^3 - 3(x^2)(2) + 3(x)(2^2) - (2)^3$
$(x - 2)^3 = x^3 - 6x^2 + 3(x)(4) - 8$
$(x - 2)^3 = x^3 - 6x^2 + 12x - 8$ [Applying the identity $(a-b)^3$]
Step 3: Equating LHS and RHS
Substitute the expanded RHS back into the original equation:
$x^3 - 4x^2 - x + 1 = x^3 - 6x^2 + 12x - 8$
Step 4: Simplifying the equation
To simplify, we bring all terms to the left-hand side (LHS):
$(x^3 - 4x^2 - x + 1) - (x^3 - 6x^2 + 12x - 8) = 0$
$x^3 - 4x^2 - x + 1 - x^3 + 6x^2 - 12x + 8 = 0$ [Distributing the negative sign]
Step 5: Combining like terms
Group the terms by their powers of $x$:
$(x^3 - x^3) + (-4x^2 + 6x^2) + (-x - 12x) + (1 + 8) = 0$
$0x^3 + 2x^2 - 13x + 9 = 0$
$2x^2 - 13x + 9 = 0$
Step 6: Conclusion
The resulting equation is $2x^2 - 13x + 9 = 0$. This equation is in the form $ax^2 + bx + c = 0$, where $a = 2$, $b = -13$, and $c = 9$. Since the highest degree of the variable $x$ is 2 and $a \neq 0$, the equation satisfies the definition of a quadratic equation.
Final Answer: Yes, the given equation is a quadratic equation.
Solution:
Given:
1. The shape of the plot is rectangular.
2. The area of the rectangular plot ($A$) = $528$ $m^2$.
3. The relationship between length ($l$) and breadth ($b$): The length is one more than twice its breadth.
To Find:
Represent the given situation in the form of a quadratic equation.
Step 1: Defining the Variables
Let the breadth of the rectangular plot be $x$ metres.
According to the problem, the length is one more than twice the breadth.
Therefore, the length of the plot $l = (2x + 1)$ metres.
Step 2: Applying the Formula for Area
The area of a rectangle is given by the formula:
$Area = Length \times Breadth$
$A = l \times b$
Step 3: Formulating the Equation
Substitute the given values and the expressions defined in Step 1 into the area formula:
$528 = (2x + 1) \times x$
Step 4: Simplifying the Expression
Distribute $x$ into the parentheses:
$528 = 2x^2 + x$
Step 5: Rearranging into Standard Quadratic Form
The standard form of a quadratic equation is $ax^2 + bx + c = 0$.
Subtract $528$ from both sides of the equation:
$2x^2 + x - 528 = 0$
Justification:
The equation $2x^2 + x - 528 = 0$ is a quadratic equation because it is a polynomial equation of degree 2, where $a = 2$, $b = 1$, and $c = -528$.
Final Answer: The quadratic equation representing the situation is $2x^2 + x - 528 = 0$, where $x$ represents the breadth of the plot in metres.
Solution:
Given:
To Find:
Represent the given situation in the form of a quadratic equation in terms of the speed of the train.
Step 1: Defining Variables
Let the uniform speed of the train be $x$ km/h.
We know the fundamental relationship between distance, speed, and time is given by the formula:
$\text{Time} = \frac{\text{Distance}}{\text{Speed}}$
Step 2: Formulating Time Expressions
Case 1: When the train travels at the original uniform speed $x$ km/h.
Time taken ($t_1$) = $\frac{480}{x}$ hours.
Case 2: When the speed is reduced by $8$ km/h.
New speed = $(x - 8)$ km/h.
Time taken ($t_2$) = $\frac{480}{x - 8}$ hours.
Step 3: Establishing the Relationship
According to the problem, the train takes $3$ hours more when the speed is reduced. Therefore, the difference between the new time ($t_2$) and the original time ($t_1$) is $3$ hours:
$t_2 - t_1 = 3$
Substituting the expressions from Step 2:
$\frac{480}{x - 8} - \frac{480}{x} = 3$
Step 4: Simplifying the Equation
Divide the entire equation by $3$ to simplify the coefficients:
$\frac{160}{x - 8} - \frac{160}{x} = 1$
Find a common denominator for the left-hand side, which is $x(x - 8)$:
$\frac{160x - 160(x - 8)}{x(x - 8)} = 1$
Expand the numerator:
$\frac{160x - 160x + 1280}{x^2 - 8x} = 1$
Simplify the numerator ($160x - 160x = 0$):
$\frac{1280}{x^2 - 8x} = 1$
Step 5: Final Algebraic Form
Multiply both sides by $(x^2 - 8x)$:
$1280 = x^2 - 8x$
Rearrange the terms to the standard form of a quadratic equation $ax^2 + bx + c = 0$:
$x^2 - 8x - 1280 = 0$
Final Answer: The quadratic equation representing the situation is $x^2 - 8x - 1280 = 0$, where $x$ is the speed of the train in km/h.
Solution:
Given:
1. Rohan’s mother is $26$ years older than Rohan.
2. The product of their ages $3$ years from now will be $360$.
To Find:
Represent the given situation in the form of a quadratic equation in terms of Rohan's present age.
Step 1: Defining the Variables
Let the present age of Rohan be $x$ years.
Since Rohan’s mother is $26$ years older than him, the present age of Rohan’s mother is $(x + 26)$ years.
Step 2: Determining Ages 3 Years from Now
After $3$ years, the age of each person will increase by $3$ years.
Rohan’s age after $3$ years = $(x + 3)$ years.
Rohan’s mother’s age after $3$ years = $(x + 26) + 3 = (x + 29)$ years.
Step 3: Formulating the Equation
According to the problem, the product of their ages $3$ years from now is $360$.
Therefore, we set up the equation:
$(x + 3)(x + 29) = 360$
Step 4: Expanding and Simplifying the Equation
Using the distributive property (FOIL method) to expand the left side:
$x(x + 29) + 3(x + 29) = 360$
$x^2 + 29x + 3x + 87 = 360$
[Combining like terms $29x$ and $3x$]:
$x^2 + 32x + 87 = 360$
Step 5: Bringing the Equation to Standard Form
The standard form of a quadratic equation is $ax^2 + bx + c = 0$. Subtract $360$ from both sides:
$x^2 + 32x + 87 - 360 = 0$
$x^2 + 32x - 273 = 0$
Justification:
The resulting equation $x^2 + 32x - 273 = 0$ is a polynomial of degree $2$, which satisfies the definition of a quadratic equation where $a=1$, $b=32$, and $c=-273$.
Final Answer: The quadratic equation representing the situation is $x^2 + 32x - 273 = 0$, where $x$ is Rohan's present age.
Solution:
Given: The algebraic equation $(x - 3)(2x + 1) = x(x + 5)$.
To Find: Determine whether the given equation is a quadratic equation.
Definition: A quadratic equation is an equation of the form $ax^2 + bx + c = 0$, where $a, b, c$ are real numbers and $a \neq 0$. The highest power (degree) of the variable in a quadratic equation must be 2.
Step 1: Expanding the Left-Hand Side (LHS)
The LHS is $(x - 3)(2x + 1)$. We apply the distributive property (FOIL method):
$(x - 3)(2x + 1) = x(2x) + x(1) - 3(2x) - 3(1)$
$= 2x^2 + x - 6x - 3$
$= 2x^2 - 5x - 3$ [Combining like terms $x$ and $-6x$]
Step 2: Expanding the Right-Hand Side (RHS)
The RHS is $x(x + 5)$. We apply the distributive property:
$x(x + 5) = x(x) + x(5)$
$= x^2 + 5x$
Step 3: Equating LHS and RHS and Simplifying
Now, set the expanded LHS equal to the expanded RHS:
$2x^2 - 5x - 3 = x^2 + 5x$
To bring the equation into the standard form $ax^2 + bx + c = 0$, we subtract $(x^2 + 5x)$ from both sides:
$(2x^2 - x^2) + (-5x - 5x) - 3 = 0$
$x^2 - 10x - 3 = 0$
Step 4: Verification against the Standard Form
Comparing $x^2 - 10x - 3 = 0$ with the standard form $ax^2 + bx + c = 0$:
Here, $a = 1$, $b = -10$, and $c = -3$.
Since $a \neq 0$ and the highest degree of the variable $x$ is 2, the equation satisfies the definition of a quadratic equation.
Final Answer: Yes, the given equation $(x - 3)(2x + 1) = x(x + 5)$ is a quadratic equation because it simplifies to the form $x^2 - 10x - 3 = 0$.
Solution:
Given: The product of two consecutive positive integers is $306$.
To find: Represent the given situation in the form of a quadratic equation.
Step 1: Defining the variables
Let the first positive integer be $x$.
Since the integers are consecutive, the next integer must be $x + 1$.
[Assumption: $x$ is a positive integer, therefore $x > 0$].
Step 2: Formulating the equation based on the given condition
According to the problem, the product of these two consecutive integers is $306$.
Mathematically, this is expressed as:
$x(x + 1) = 306$
Step 3: Expanding the expression
Distribute $x$ into the parentheses:
$x^2 + x = 306$
Step 4: Rearranging into standard quadratic form
A quadratic equation is represented in the standard form $ax^2 + bx + c = 0$.
Subtract $306$ from both sides of the equation to set the right side to zero:
$x^2 + x - 306 = 0$
Step 5: Verification of the form
Comparing $x^2 + x - 306 = 0$ with the standard form $ax^2 + bx + c = 0$:
Here, $a = 1$, $b = 1$, and $c = -306$.
Since the highest power of the variable $x$ is $2$, this is a quadratic equation.
Final Answer: The quadratic equation representing the given situation is $x^2 + x - 306 = 0$, where $x$ is the smaller integer.
Solution:
Given: The algebraic equation $(x + 2)^3 = 2x(x^2 - 1)$.
To Find: Determine whether the given equation is a quadratic equation.
Definition: A quadratic equation in the variable $x$ is an equation of the form $ax^2 + bx + c = 0$, where $a, b, c$ are real numbers and $a \neq 0$. The highest power (degree) of the variable $x$ must be exactly 2.
Step 1: Expanding the Left-Hand Side (LHS)
The LHS is $(x + 2)^3$. We use the algebraic identity for the cube of a binomial: $(a + b)^3 = a^3 + 3a^2b + 3ab^2 + b^3$.
Here, $a = x$ and $b = 2$.
$(x + 2)^3 = x^3 + 3(x^2)(2) + 3(x)(2^2) + 2^3$
$= x^3 + 6x^2 + 3(x)(4) + 8$
$= x^3 + 6x^2 + 12x + 8$ [Expanding the terms]
Step 2: Expanding the Right-Hand Side (RHS)
The RHS is $2x(x^2 - 1)$. We use the distributive property of multiplication over subtraction: $a(b - c) = ab - ac$.
$2x(x^2 - 1) = (2x \cdot x^2) - (2x \cdot 1)$
$= 2x^3 - 2x$ [Distributing $2x$ into the parentheses]
Step 3: Equating LHS and RHS and Simplifying
Now, set the expanded LHS equal to the expanded RHS:
$x^3 + 6x^2 + 12x + 8 = 2x^3 - 2x$
To bring all terms to one side, subtract $(2x^3 - 2x)$ from both sides:
$x^3 - 2x^3 + 6x^2 + 12x + 2x + 8 = 0$
$-x^3 + 6x^2 + 14x + 8 = 0$ [Combining like terms]
Step 4: Analyzing the Degree of the Equation
The resulting equation is $-x^3 + 6x^2 + 14x + 8 = 0$.
The highest power (degree) of the variable $x$ in this equation is 3. [Since the term $-x^3$ exists and its coefficient is non-zero].
Conclusion:
Since the degree of the equation is 3, it is a cubic equation, not a quadratic equation. A quadratic equation must have a maximum degree of 2.
Final Answer: The given equation $(x + 2)^3 = 2x(x^2 - 1)$ is not a quadratic equation.
Solution:
Given: The equation $x^2 - 2x = (-2)(3 - x)$.
To Find: Determine whether the given equation is a quadratic equation.
Definition: A quadratic equation in the variable $x$ is an equation of the form $ax^2 + bx + c = 0$, where $a, b, c$ are real numbers and $a \neq 0$.
Step 1: Simplify the right-hand side (RHS) of the equation.
The given equation is:
$x^2 - 2x = (-2)(3 - x)$
Applying the distributive property of multiplication over subtraction, $a(b - c) = ab - ac$:
$x^2 - 2x = (-2 \times 3) - (-2 \times x)$
$x^2 - 2x = -6 + 2x$
Step 2: Rearrange the equation into the standard form $ax^2 + bx + c = 0$.
To bring all terms to the left-hand side, subtract $2x$ and add $6$ to both sides of the equation:
$x^2 - 2x - 2x + 6 = 0$
Combine the like terms ($-2x$ and $-2x$):
$x^2 - 4x + 6 = 0$
Step 3: Compare with the standard form.
Comparing $x^2 - 4x + 6 = 0$ with the standard quadratic form $ax^2 + bx + c = 0$:
Here, $a = 1$, $b = -4$, and $c = 6$.
[Since $a = 1 \neq 0$, the equation satisfies the condition for being a quadratic equation.]
Conclusion:
Since the highest power of the variable $x$ in the simplified equation is $2$, and the coefficient of $x^2$ is non-zero, the given equation is a quadratic equation.
Final Answer: Yes, the given equation $x^2 - 2x = (-2)(3 - x)$ is a quadratic equation.
Solution:
Given: The equation $x^2 + 3x + 1 = (x - 2)^2$.
To Find: Determine whether the given equation is a quadratic equation.
Definition: A quadratic equation in the variable $x$ is an equation of the form $ax^2 + bx + c = 0$, where $a, b, c$ are real numbers and $a \neq 0$.
Step 1: Expand the right-hand side of the equation.
The given equation is:
$x^2 + 3x + 1 = (x - 2)^2$
We use the algebraic identity $(a - b)^2 = a^2 - 2ab + b^2$. Here, $a = x$ and $b = 2$.
$(x - 2)^2 = x^2 - 2(x)(2) + (2)^2$
$(x - 2)^2 = x^2 - 4x + 4$
Step 2: Substitute the expanded form back into the original equation.
$x^2 + 3x + 1 = x^2 - 4x + 4$
Step 3: Rearrange the terms to one side to set the equation to zero.
Subtract $(x^2 - 4x + 4)$ from both sides of the equation:
$x^2 + 3x + 1 - (x^2 - 4x + 4) = 0$
$x^2 + 3x + 1 - x^2 + 4x - 4 = 0$
Step 4: Simplify the expression by combining like terms.
Group the $x^2$ terms, the $x$ terms, and the constant terms:
$(x^2 - x^2) + (3x + 4x) + (1 - 4) = 0$
$0x^2 + 7x - 3 = 0$
$7x - 3 = 0$
Step 5: Analyze the resulting equation.
The simplified equation is $7x - 3 = 0$. This is a linear equation because the highest power of the variable $x$ is 1. Comparing this to the standard form $ax^2 + bx + c = 0$, we see that the coefficient of $x^2$ (which is $a$) is $0$. Since a quadratic equation must have $a \neq 0$, this equation does not satisfy the definition.
Final Answer: The given equation $x^2 + 3x + 1 = (x - 2)^2$ is not a quadratic equation because the $x^2$ terms cancel out, leaving a linear equation.
Solution:
Given: The equation $(x + 1)^2 = 2(x - 3)$.
To Find: Determine whether the given equation is a quadratic equation.
Definition: A quadratic equation in the variable $x$ is an equation of the form $ax^2 + bx + c = 0$, where $a, b, c$ are real numbers and $a \neq 0$.
Step 1: Expanding the left-hand side (LHS) of the equation.
The expression is $(x + 1)^2$. We use the algebraic identity $(a + b)^2 = a^2 + 2ab + b^2$.
Substituting $a = x$ and $b = 1$:
$(x + 1)^2 = x^2 + 2(x)(1) + (1)^2$
$(x + 1)^2 = x^2 + 2x + 1$
Step 2: Expanding the right-hand side (RHS) of the equation.
The expression is $2(x - 3)$. We use the distributive property $a(b - c) = ab - ac$.
$2(x - 3) = 2(x) - 2(3)$
$2(x - 3) = 2x - 6$
Step 3: Equating the expanded sides and simplifying.
Equating the results from Step 1 and Step 2:
$x^2 + 2x + 1 = 2x - 6$
Step 4: Bringing all terms to one side to form the standard quadratic form.
Subtract $2x$ from both sides:
$x^2 + 2x - 2x + 1 = -6$
$x^2 + 1 = -6$
Add $6$ to both sides:
$x^2 + 1 + 6 = 0$
$x^2 + 7 = 0$
Step 5: Comparing with the standard form $ax^2 + bx + c = 0$.
The equation $x^2 + 7 = 0$ can be written as $1x^2 + 0x + 7 = 0$.
Here, $a = 1$, $b = 0$, and $c = 7$.
Since $a \neq 0$ (as $1 \neq 0$), the equation satisfies the condition for being a quadratic equation.
Final Answer: Yes, the given equation $(x + 1)^2 = 2(x - 3)$ is a quadratic equation because it can be simplified to the form $ax^2 + bx + c = 0$ where $a \neq 0$.
Solution:
Given: The equation $(2x - 1)(x - 3) = (x + 5)(x - 1)$.
To Find: Determine whether the given equation is a quadratic equation.
Definition: A quadratic equation in the variable $x$ is an equation of the form $ax^2 + bx + c = 0$, where $a, b, c$ are real numbers and $a \neq 0$.
Step 1: Expanding the Left-Hand Side (LHS)
The LHS is $(2x - 1)(x - 3)$. We apply the distributive property (FOIL method):
$(2x - 1)(x - 3) = 2x(x) + 2x(-3) - 1(x) - 1(-3)$
$= 2x^2 - 6x - x + 3$
$= 2x^2 - 7x + 3$ [Combining like terms $-6x$ and $-x$]
Step 2: Expanding the Right-Hand Side (RHS)
The RHS is $(x + 5)(x - 1)$. We apply the distributive property:
$(x + 5)(x - 1) = x(x) + x(-1) + 5(x) + 5(-1)$
$= x^2 - x + 5x - 5$
$= x^2 + 4x - 5$ [Combining like terms $-x$ and $5x$]
Step 3: Equating LHS and RHS and Simplifying
Now, set the expanded LHS equal to the expanded RHS:
$2x^2 - 7x + 3 = x^2 + 4x - 5$
To bring the equation into the standard form $ax^2 + bx + c = 0$, subtract $(x^2 + 4x - 5)$ from both sides:
$2x^2 - x^2 - 7x - 4x + 3 + 5 = 0$
$x^2 - 11x + 8 = 0$
Step 4: Verification against the Standard Form
The resulting equation is $x^2 - 11x + 8 = 0$.
Comparing this with the standard form $ax^2 + bx + c = 0$:
Here, $a = 1$, $b = -11$, and $c = 8$.
Since $a = 1 \neq 0$, the equation satisfies the condition for being a quadratic equation.
Final Answer: Yes, the given equation $(2x - 1)(x - 3) = (x + 5)(x - 1)$ is a quadratic equation.