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CBSE - Class 10 Mathematics Quadratic Equations Worksheet

EXERCISE 4.1

1.
Check whether the following are quadratic equations : (iii) $(x – 2)(x + 1) = (x – 1)(x + 3)$
2.
Check whether the following are quadratic equations : (viii) $x^3 – 4x^2 – x + 1 = (x – 2)^3$
3.
Represent the following situations in the form of quadratic equations : (i) The area of a rectangular plot is $528$ $m^2$. The length of the plot (in metres) is one more than twice its breadth. We need to find the length and breadth of the plot.
4.
Represent the following situations in the form of quadratic equations : (iv) A train travels a distance of $480$ km at a uniform speed. If the speed had been $8$ km/h less, then it would have taken $3$ hours more to cover the same distance. We need to find the speed of the train.
5.
Represent the following situations in the form of quadratic equations : (iii) Rohan’s mother is $26$ years older than him. The product of their ages (in years) $3$ years from now will be $360$. We would like to find Rohan’s present age.
6.
Check whether the following are quadratic equations : (iv) $(x – 3)(2x +1) = x(x + 5)$
7.
Represent the following situations in the form of quadratic equations : (ii) The product of two consecutive positive integers is $306$. We need to find the integers.
8.
Check whether the following are quadratic equations : (vii) $(x + 2)^3 = 2x (x^2 – 1)$
9.
Check whether the following are quadratic equations : (ii) $x^2 – 2x = (–2)(3 – x)$
10.
Check whether the following are quadratic equations : (vi) $x^2 + 3x + 1 = (x – 2)^2$
11.
Check whether the following are quadratic equations : (i) $(x + 1)^2 = 2(x – 3)$
12.
Check whether the following are quadratic equations : (v) $(2x – 1)(x – 3) = (x + 5)(x – 1)$

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.

Length (l) Breadth (b)

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:

  • Total distance to be covered by the train, $d = 480$ km.
  • The train travels at a uniform speed.
  • If the speed were $8$ km/h less, the time taken to cover the same distance would increase by $3$ hours.

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.

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