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CBSE - Class 10 Mathematics Quadratic Equations Worksheet
EXERCISE 4.3
Worksheet Answers
Solution:
Given: A quadratic equation $kx(x - 2) + 6 = 0$, where $k \neq 0$.
To Find: The value(s) of $k$ such that the quadratic equation has two equal real roots.
Step 1: Simplifying the equation into standard form
The standard form of a quadratic equation is $ax^2 + bx + c = 0$. We expand the given equation:
$kx(x - 2) + 6 = 0$
$kx^2 - 2kx + 6 = 0$
[Distributive property of multiplication over subtraction]
Step 2: Identifying coefficients
Comparing $kx^2 - 2kx + 6 = 0$ with $ax^2 + bx + c = 0$, we identify:
$a = k$
$b = -2k$
$c = 6$
Step 3: Applying the condition for equal roots
For a quadratic equation to have two equal real roots, its discriminant ($D$) must be equal to zero.
Formula: $D = b^2 - 4ac = 0$
Substituting the identified coefficients into the discriminant formula:
$(-2k)^2 - 4(k)(6) = 0$
Step 4: Solving for $k$
$4k^2 - 24k = 0$
[Simplifying the powers and products]
Factor out the common term $4k$:
$4k(k - 6) = 0$
[Using the zero-product property: if $p \cdot q = 0$, then $p=0$ or $q=0$]
Case 1: $4k = 0 \implies k = 0$
Case 2: $k - 6 = 0 \implies k = 6$
Step 5: Verification of validity
If $k = 0$, the equation becomes $0x^2 - 2(0)x + 6 = 0$, which simplifies to $6 = 0$. This is a contradiction and not a quadratic equation. Therefore, $k$ cannot be $0$.
If $k = 6$, the equation becomes $6x^2 - 12x + 6 = 0$. Dividing by 6, we get $x^2 - 2x + 1 = 0$, which is $(x - 1)^2 = 0$, yielding equal roots $x = 1, 1$.
Final Answer: The value of $k$ is 6.
Solution:
Given:
1. The sum of the ages of two friends is $20$ years.
2. Four years ago, the product of their ages was $48$.
To Find:
Determine if the situation is possible, and if so, find the present ages of the two friends.
Step 1: Defining Variables
Let the present age of the first friend be $x$ years.
Since the sum of their ages is $20$ years, the present age of the second friend is $(20 - x)$ years.
Step 2: Formulating the Equation based on the condition "Four years ago"
Age of the first friend four years ago = $(x - 4)$ years.
Age of the second friend four years ago = $(20 - x - 4) = (16 - x)$ years.
According to the problem, the product of these ages is $48$:
$(x - 4)(16 - x) = 48$
Step 3: Expanding and Simplifying the Equation
Expanding the left side using the distributive property:
$x(16) - x(x) - 4(16) + 4(x) = 48$
$16x - x^2 - 64 + 4x = 48$
$-x^2 + 20x - 64 = 48$
Rearranging the terms to form a standard quadratic equation $ax^2 + bx + c = 0$:
$-x^2 + 20x - 64 - 48 = 0$
$-x^2 + 20x - 112 = 0$
Multiplying by $-1$ to make the leading coefficient positive:
$x^2 - 20x + 112 = 0$
Step 4: Checking for the possibility of the situation
To determine if the situation is possible, we calculate the discriminant ($D$) of the quadratic equation $ax^2 + bx + c = 0$, where $a = 1$, $b = -20$, and $c = 112$.
The formula for the discriminant is $D = b^2 - 4ac$.
$D = (-20)^2 - 4(1)(112)$
$D = 400 - 448$
$D = -48$
Step 5: Conclusion based on the Discriminant
[Since the discriminant $D < 0$, the quadratic equation has no real roots.]
Because the roots are not real, it is impossible to find real values for the ages of the friends that satisfy the given conditions.
Final Answer: The situation is not possible.
Solution:
Given:
1. The shape of the mango grove is rectangular.
2. The length ($l$) of the grove is twice its breadth ($b$), i.e., $l = 2b$.
3. The area ($A$) of the rectangular grove is $800$ $m^2$.
To Find:
1. Determine if such a rectangular grove can be designed.
2. If possible, find the length ($l$) and breadth ($b$).
Visual Representation:
Step 1: Formulating the Algebraic Equation
Let the breadth of the rectangular mango grove be $b$ meters.
According to the problem, the length $l$ is twice the breadth, so $l = 2b$ meters.
The formula for the area of a rectangle is: $Area = length \times breadth$.
Substituting the given values into the formula:
$800 = (2b) \times (b)$
$800 = 2b^2$
Step 2: Simplifying the Quadratic Equation
Divide both sides of the equation by $2$:
$\frac{800}{2} = \frac{2b^2}{2}$
$400 = b^2$
Rearranging into the standard quadratic form $ax^2 + bx + c = 0$:
$b^2 - 400 = 0$
Step 3: Determining Possibility using the Discriminant
To check if real roots exist, we calculate the discriminant ($D$) where $D = B^2 - 4AC$.
In the equation $b^2 + 0b - 400 = 0$, we have $A = 1$, $B = 0$, and $C = -400$.
$D = (0)^2 - 4(1)(-400)$
$D = 0 + 1600$
$D = 1600$
[Since $D > 0$, the quadratic equation has two distinct real roots, meaning it is possible to design the grove.]
Step 4: Solving for Breadth and Length
From $b^2 = 400$, we take the square root of both sides:
$b = \pm \sqrt{400}$
$b = \pm 20$
[Since breadth cannot be negative, we discard $b = -20$.]
Therefore, $b = 20$ meters.
Now, calculate the length $l$ using $l = 2b$:
$l = 2 \times 20 = 40$ meters.
Final Answer:
Yes, it is possible to design the mango grove. The breadth of the grove is $20$ m and the length is $40$ m.
Solution:
Given: A quadratic equation $2x^2 - 6x + 3 = 0$.
To Find: The nature of the roots of the given quadratic equation and, if real roots exist, find their values.
Step 1: Identify the coefficients of the quadratic equation.
A standard quadratic equation is represented as $ax^2 + bx + c = 0$. Comparing the given equation $2x^2 - 6x + 3 = 0$ with the standard form:
Step 2: Determine the nature of the roots using the Discriminant ($D$).
The discriminant of a quadratic equation is given by the formula $D = b^2 - 4ac$.
Substituting the values of $a$, $b$, and $c$:
$D = (-6)^2 - 4(2)(3)$
$D = 36 - 24$
$D = 12$
[Since $D > 0$, the quadratic equation has two distinct real roots.]
Step 3: Apply the Quadratic Formula to find the roots.
The quadratic formula is given by $x = \frac{-b \pm \sqrt{D}}{2a}$.
Substituting the known values into the formula:
$x = \frac{-(-6) \pm \sqrt{12}}{2(2)}$
$x = \frac{6 \pm \sqrt{4 \times 3}}{4}$
$x = \frac{6 \pm 2\sqrt{3}}{4}$
Step 4: Simplify the expression.
Factor out the common term $2$ from the numerator:
$x = \frac{2(3 \pm \sqrt{3})}{4}$
$x = \frac{3 \pm \sqrt{3}}{2}$
Therefore, the two roots are:
$x_1 = \frac{3 + \sqrt{3}}{2}$
$x_2 = \frac{3 - \sqrt{3}}{2}$
Final Answer: The roots are real and distinct. The roots of the equation are $\frac{3 + \sqrt{3}}{2}$ and $\frac{3 - \sqrt{3}}{2}$.
Solution:
Given: A quadratic equation $3x^2 - 4\sqrt{3}x + 4 = 0$.
To Find: The nature of the roots and the roots themselves if they exist.
Step 1: Identify the coefficients of the quadratic equation.
The standard form of a quadratic equation is $ax^2 + bx + c = 0$. Comparing the given equation $3x^2 - 4\sqrt{3}x + 4 = 0$ with the standard form, we identify:
$a = 3$
$b = -4\sqrt{3}$
$c = 4$
Step 2: Determine the nature of the roots using the Discriminant ($D$).
The discriminant is given by the formula $D = b^2 - 4ac$.
Substituting the values identified in Step 1:
$D = (-4\sqrt{3})^2 - 4(3)(4)$
$D = (16 \times 3) - 48$
$D = 48 - 48$
$D = 0$
[Since $D = 0$, the quadratic equation has two equal real roots.]
Step 3: Calculate the roots using the Quadratic Formula.
The quadratic formula is given by $x = \frac{-b \pm \sqrt{D}}{2a}$.
Since $D = 0$, the formula simplifies to $x = \frac{-b}{2a}$.
Substituting the values:
$x = \frac{-(-4\sqrt{3})}{2(3)}$
$x = \frac{4\sqrt{3}}{6}$
Step 4: Simplify the expression.
$x = \frac{4\sqrt{3}}{6}$
Dividing both the numerator and the denominator by their greatest common divisor, which is $2$:
$x = \frac{2\sqrt{3}}{3}$
Since the roots are equal, both roots are $\frac{2\sqrt{3}}{3}$.
[Note: $\frac{2\sqrt{3}}{3}$ can also be written as $\frac{2}{\sqrt{3}}$ by rationalizing the denominator.]
Final Answer: The roots are real and equal, and the roots are $\frac{2\sqrt{3}}{3}, \frac{2\sqrt{3}}{3}$.
Solution:
Given: A quadratic equation $2x^2 - 3x + 5 = 0$.
To Find: The nature of the roots of the given quadratic equation and, if real roots exist, to determine their values.
Step 1: Identify the coefficients of the quadratic equation.
A standard quadratic equation is represented as $ax^2 + bx + c = 0$.
Comparing the given equation $2x^2 - 3x + 5 = 0$ with the standard form:
$a = 2$
$b = -3$
$c = 5$
Step 2: Determine the nature of the roots using the Discriminant ($D$).
The discriminant of a quadratic equation is given by the formula:
$D = b^2 - 4ac$
Substituting the values of $a$, $b$, and $c$ into the formula:
$D = (-3)^2 - 4(2)(5)$
$D = 9 - 40$
$D = -31$
Step 3: Analyze the nature of the roots based on the value of $D$.
According to the theory of quadratic equations:
1. If $D > 0$, the equation has two distinct real roots.
2. If $D = 0$, the equation has two equal real roots.
3. If $D < 0$, the equation has no real roots (the roots are complex/imaginary).
Since $D = -31$, and $-31 < 0$, the discriminant is negative.
Step 4: Conclusion regarding the existence of real roots.
Because the discriminant is less than zero ($D < 0$), the square root of the discriminant would result in an imaginary number. Therefore, the quadratic equation $2x^2 - 3x + 5 = 0$ does not possess any real roots.
Final Answer: The discriminant is $-31$, which is less than $0$. Therefore, the given quadratic equation has no real roots.
Solution:
Given: A quadratic equation $2x^2 + kx + 3 = 0$.
To find: The value(s) of $k$ such that the given quadratic equation has two equal real roots.
Step 1: Identify the coefficients of the quadratic equation.
A standard quadratic equation is represented as $ax^2 + bx + c = 0$. Comparing the given equation $2x^2 + kx + 3 = 0$ with the standard form, we identify:
$a = 2$
$b = k$
$c = 3$
Step 2: State the condition for equal roots.
For a quadratic equation $ax^2 + bx + c = 0$, the nature of the roots is determined by the discriminant, denoted by $D$, where $D = b^2 - 4ac$.
The condition for a quadratic equation to have two equal real roots is that the discriminant must be equal to zero:
$D = b^2 - 4ac = 0$
Step 3: Substitute the coefficients into the discriminant formula.
Substituting $a = 2$, $b = k$, and $c = 3$ into the equation $b^2 - 4ac = 0$:
$(k)^2 - 4(2)(3) = 0$
Step 4: Solve the resulting equation for $k$.
Perform the multiplication inside the expression:
$k^2 - 24 = 0$
Isolate $k^2$ by adding 24 to both sides of the equation:
$k^2 = 24$
Take the square root of both sides to solve for $k$:
$k = \pm\sqrt{24}$
Simplify the radical expression $\sqrt{24}$:
$\sqrt{24} = \sqrt{4 \times 6} = \sqrt{4} \times \sqrt{6} = 2\sqrt{6}$
Therefore:
$k = \pm 2\sqrt{6}$
Step 5: Conclusion.
The values of $k$ for which the quadratic equation $2x^2 + kx + 3 = 0$ has two equal roots are $2\sqrt{6}$ and $-2\sqrt{6}$.
Final Answer: k = 2\sqrt{6}, -2\sqrt{6}
Solution:
Given:
Perimeter of the rectangular park ($P$) = $80$ m.
Area of the rectangular park ($A$) = $400$ m$^2$.
To Find:
Determine if such a park can be designed, and if so, find its length ($l$) and breadth ($b$).
Step 1: Formulating the Equations
Let the length of the rectangular park be $l$ meters and the breadth be $b$ meters.
The formula for the perimeter of a rectangle is $P = 2(l + b)$.
Given $P = 80$, we have:
$2(l + b) = 80$
$l + b = 40$
$b = 40 - l$ --- (Equation 1)
The formula for the area of a rectangle is $A = l \times b$.
Given $A = 400$, we have:
$l \times b = 400$ --- (Equation 2)
Step 2: Substituting Equation 1 into Equation 2
Substitute $b = 40 - l$ into the area equation:
$l(40 - l) = 400$
$40l - l^2 = 400$
Rearranging the terms to form a standard quadratic equation $ax^2 + bx + c = 0$:
$l^2 - 40l + 400 = 0$
Step 3: Checking the Discriminant
To determine if the roots are real, we calculate the discriminant ($D = b^2 - 4ac$).
Here, $a = 1$, $b = -40$, and $c = 400$.
$D = (-40)^2 - 4(1)(400)$
$D = 1600 - 1600$
$D = 0$
[Since $D = 0$, the quadratic equation has two equal real roots, meaning it is possible to design such a park.]
Step 4: Solving for $l$
Using the quadratic formula $l = \frac{-b \pm \sqrt{D}}{2a}$:
$l = \frac{-(-40) \pm \sqrt{0}}{2(1)}$
$l = \frac{40}{2}$
$l = 20$ m
Step 5: Finding the breadth $b$
Substitute $l = 20$ into Equation 1:
$b = 40 - 20$
$b = 20$ m
Conclusion:
Since the length and breadth are equal, the rectangular park is a square with side length $20$ m.
Final Answer: Yes, it is possible to design the park. The length is 20 m and the breadth is 20 m.