Quadratic Equations | Exercise 4.2

Question 1

Find the roots of the following quadratic equations by factorisation:

(i) x23x10=0x^2 - 3x - 10 = 0

(ii) 2x2+x6=02x^2 + x - 6 = 0

(iii) 2x2+7x+52=0\sqrt{2}x^2 + 7x + 5\sqrt{2} = 0

(iv) 2x2x+18=02x^2 - x + \frac{1}{8} = 0

(v) 100x220x+1=0100x^2 - 20x + 1 = 0

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Solution

We will factorize each quadratic equation to find its roots.

Step 1 — Factorize x23x10=0x^2 - 3x - 10 = 0

We need to split the middle term. The product of 1 and -10 is -10. We need two numbers that multiply to -10. They must add to -3. The numbers are -5 and 2. x25x+2x10=0x^2 - 5x + 2x - 10 = 0 We group the terms. x(x5)+2(x5)=0x(x - 5) + 2(x - 5) = 0 We factor out the common term. (x5)(x+2)=0(x - 5)(x + 2) = 0

Step 2 — Find the roots for (i)

We set each factor to zero. x5=0orx+2=0x - 5 = 0 \quad \text{or} \quad x + 2 = 0 We solve for xx. x=5orx=2x = 5 \quad \text{or} \quad x = -2

x=5,2\boxed{x = 5, -2}

Step 3 — Factorize 2x2+x6=02x^2 + x - 6 = 0

We need to split the middle term. The product of 2 and -6 is -12. We need two numbers that multiply to -12. They must add to -1. The numbers are -4 and 3. 2x24x+3x6=02x^2 - 4x + 3x - 6 = 0 We group the terms. 2x(x2)+3(x2)=02x(x - 2) + 3(x - 2) = 0 We factor out the common term. (x2)(2x+3)=0(x - 2)(2x + 3) = 0

Step 4 — Find the roots for (ii)

We set each factor to zero. x2=0or2x+3=0x - 2 = 0 \quad \text{or} \quad 2x + 3 = 0 We solve for xx. x=2or2x=3x = 2 \quad \text{or} \quad 2x = -3 x=2orx=32x = 2 \quad \text{or} \quad x = -\frac{3}{2}

x=2,32\boxed{x = 2, -\frac{3}{2}}

Step 5 — Factorize 2x2+7x+52=0\sqrt{2}x^2 + 7x + 5\sqrt{2} = 0

We need to split the middle term. The product of 2\sqrt{2} and 525\sqrt{2} is 10. We need two numbers that multiply to 10. They must add to 7. The numbers are 5 and 2. 2x2+5x+2x+52=0\sqrt{2}x^2 + 5x + 2x + 5\sqrt{2} = 0 We group the terms. x(2x+5)+2(2x+5)=0x(\sqrt{2}x + 5) + \sqrt{2}(\sqrt{2}x + 5) = 0 We factor out the common term. (2x+5)(x+2)=0(\sqrt{2}x + 5)(x + \sqrt{2}) = 0

Step 6 — Find the roots for (iii)

We set each factor to zero. 2x+5=0orx+2=0\sqrt{2}x + 5 = 0 \quad \text{or} \quad x + \sqrt{2} = 0 We solve for xx. 2x=5orx=2\sqrt{2}x = -5 \quad \text{or} \quad x = -\sqrt{2} x=52orx=2x = -\frac{5}{\sqrt{2}} \quad \text{or} \quad x = -\sqrt{2}

x=52,2\boxed{x = -\frac{5}{\sqrt{2}}, -\sqrt{2}}

Step 7 — Factorize 2x2x+18=02x^2 - x + \frac{1}{8} = 0

First, we clear the fraction. We multiply the entire equation by 8. 16x28x+1=016x^2 - 8x + 1 = 0 We need to split the middle term. The product of 16 and 1 is 16. We need two numbers that multiply to 16. They must add to -8. The numbers are -4 and -4. 16x24x4x+1=016x^2 - 4x - 4x + 1 = 0 We group the terms. 4x(4x1)1(4x1)=04x(4x - 1) - 1(4x - 1) = 0 We factor out the common term. (4x1)(4x1)=0(4x - 1)(4x - 1) = 0

Step 8 — Find the roots for (iv)

We set each factor to zero. 4x1=0or4x1=04x - 1 = 0 \quad \text{or} \quad 4x - 1 = 0 We solve for xx. 4x=1or4x=14x = 1 \quad \text{or} \quad 4x = 1 x=14orx=14x = \frac{1}{4} \quad \text{or} \quad x = \frac{1}{4}

x=14,14\boxed{x = \frac{1}{4}, \frac{1}{4}}

Step 9 — Factorize 100x220x+1=0100x^2 - 20x + 1 = 0

We need to split the middle term. The product of 100 and 1 is 100. We need two numbers that multiply to 100. They must add to -20. The numbers are -10 and -10. 100x210x10x+1=0100x^2 - 10x - 10x + 1 = 0 We group the terms. 10x(10x1)1(10x1)=010x(10x - 1) - 1(10x - 1) = 0 We factor out the common term. (10x1)(10x1)=0(10x - 1)(10x - 1) = 0

Step 10 — Find the roots for (v)

We set each factor to zero. 10x1=0or10x1=010x - 1 = 0 \quad \text{or} \quad 10x - 1 = 0 We solve for xx. 10x=1or10x=110x = 1 \quad \text{or} \quad 10x = 1 x=110orx=110x = \frac{1}{10} \quad \text{or} \quad x = \frac{1}{10}

x=110,110\boxed{x = \frac{1}{10}, \frac{1}{10}}

Answer

(i) The roots are 5 and -2. (ii) The roots are 2 and -3/2. (iii) The roots are -5/√2 and -√2. (iv) The roots are 1/4 and 1/4. (v) The roots are 1/10 and 1/10.

More questions in Exercise 4.2

Q1

Find the roots of the following quadratic equations by factorisation:

(i) x23x10=0x^2 - 3x - 10 = 0

(ii) 2x2+x6=02x^2 + x - 6 = 0

(iii) 2x2+7x+52=0\sqrt{2}x^2 + 7x + 5\sqrt{2} = 0

(iv) 2x2x+18=02x^2 - x + \frac{1}{8} = 0

(v) 100x220x+1=0100x^2 - 20x + 1 = 0

Q2

Solve the problems given in Example 1.

Q3

Find two numbers whose sum is 27 and product is 182.

Q4

Find two consecutive positive integers, sum of whose squares is 365.

Q5

The altitude of a right triangle is 7 cm less than its base. If the hypotenuse is 13 cm, find the other two sides.

Q6

A cottage industry produces a certain number of pottery articles in a day. It was observed on a particular day that the cost of production of each article (in rupees) was 3 more than twice the number of articles produced on that day. If the total cost of production on that day was ₹ 90, find the number of articles produced and the cost of each article.

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