Polynomials | Exercise 2.2

Question 2

Find a quadratic polynomial each with the given numbers as the sum and product of its zeroes respectively.

(i) 14,1\frac{1}{4}, -1

(ii) 2,13\sqrt{2}, \frac{1}{3}

(iii) 0,50, \sqrt{5}

(iv) 1,11, 1

(v) 14,14-\frac{1}{4}, \frac{1}{4}

(vi) 4,14, 1

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Solution

A quadratic polynomial can be formed using the sum and product of its zeroes.

Step 1 — Polynomial for 14,1\frac{1}{4}, -1 We use the general form for a quadratic polynomial. The general form is P(x)=x2(sum)x+(product)P(x) = x^2 - (\text{sum})x + (\text{product}). Let's substitute the given values.

P(x)=x2(14)x+(1)P(x) = x^2 - \left(\frac{1}{4}\right)x + (-1)

=x214x1= x^2 - \frac{1}{4}x - 1 We can multiply by a constant to remove fractions. Let's multiply by 4.

P(x)=4(x214x1)P(x) = 4 \left(x^2 - \frac{1}{4}x - 1\right)

=4x2x4= 4x^2 - x - 4

4x2x4\boxed{4x^2 - x - 4}

Step 2 — Polynomial for 2,13\sqrt{2}, \frac{1}{3} We use the general form for a quadratic polynomial. The general form is P(x)=x2(sum)x+(product)P(x) = x^2 - (\text{sum})x + (\text{product}). Let's substitute the given values.

P(x)=x2(2)x+(13)P(x) = x^2 - (\sqrt{2})x + \left(\frac{1}{3}\right)

=x22x+13= x^2 - \sqrt{2}x + \frac{1}{3} We can multiply by a constant to remove fractions. Let's multiply by 3.

P(x)=3(x22x+13)P(x) = 3 \left(x^2 - \sqrt{2}x + \frac{1}{3}\right)

=3x232x+1= 3x^2 - 3\sqrt{2}x + 1

3x232x+1\boxed{3x^2 - 3\sqrt{2}x + 1}

Step 3 — Polynomial for 0,50, \sqrt{5} We use the general form for a quadratic polynomial. The general form is P(x)=x2(sum)x+(product)P(x) = x^2 - (\text{sum})x + (\text{product}). Let's substitute the given values.

P(x)=x2(0)x+(5)P(x) = x^2 - (0)x + (\sqrt{5})

=x2+5= x^2 + \sqrt{5} This is our polynomial.

x2+5\boxed{x^2 + \sqrt{5}}

Step 4 — Polynomial for 1,11, 1 We use the general form for a quadratic polynomial. The general form is P(x)=x2(sum)x+(product)P(x) = x^2 - (\text{sum})x + (\text{product}). Let's substitute the given values.

P(x)=x2(1)x+(1)P(x) = x^2 - (1)x + (1)

=x2x+1= x^2 - x + 1 This is our polynomial.

x2x+1\boxed{x^2 - x + 1}

Step 5 — Polynomial for 14,14-\frac{1}{4}, \frac{1}{4} We use the general form for a quadratic polynomial. The general form is P(x)=x2(sum)x+(product)P(x) = x^2 - (\text{sum})x + (\text{product}). Let's substitute the given values.

P(x)=x2(14)x+(14)P(x) = x^2 - \left(-\frac{1}{4}\right)x + \left(\frac{1}{4}\right)

=x2+14x+14= x^2 + \frac{1}{4}x + \frac{1}{4} We can multiply by a constant to remove fractions. Let's multiply by 4.

P(x)=4(x2+14x+14)P(x) = 4 \left(x^2 + \frac{1}{4}x + \frac{1}{4}\right)

=4x2+x+1= 4x^2 + x + 1

4x2+x+1\boxed{4x^2 + x + 1}

Step 6 — Polynomial for 4,14, 1 We use the general form for a quadratic polynomial. The general form is P(x)=x2(sum)x+(product)P(x) = x^2 - (\text{sum})x + (\text{product}). Let's substitute the given values.

P(x)=x2(4)x+(1)P(x) = x^2 - (4)x + (1)

=x24x+1= x^2 - 4x + 1 This is our polynomial.

x24x+1\boxed{x^2 - 4x + 1}

Answer

(i) 4x2x44x^2 - x - 4 (ii) 3x232x+13x^2 - 3\sqrt{2}x + 1 (iii) x2+5x^2 + \sqrt{5} (iv) x2x+1x^2 - x + 1 (v) 4x2+x+14x^2 + x + 1 (vi) x24x+1x^2 - 4x + 1

More questions in Exercise 2.2

Q1

Find the zeroes of the following quadratic polynomials and verify the relationship between the zeroes and the coefficients.

(i) x22x8x^2 - 2x - 8

(ii) 4s24s+14s^2 - 4s + 1

(iii) 6x237x6x^2 - 3 - 7x

(iv) 4u2+8u4u^2 + 8u

(v) t215t^2 - 15

(vi) 3x2x43x^2 - x - 4

Q2

Find a quadratic polynomial each with the given numbers as the sum and product of its zeroes respectively.

(i) 14,1\frac{1}{4}, -1

(ii) 2,13\sqrt{2}, \frac{1}{3}

(iii) 0,50, \sqrt{5}

(iv) 1,11, 1

(v) 14,14-\frac{1}{4}, \frac{1}{4}

(vi) 4,14, 1

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