Q)  If 𝛼, β are zeroes of quadratic polynomial x2 – 2x + 3, find the polynomial whose roots are:
1. 𝛼 + 2, 𝛽 + 2
2. \frac{(\alpha - 1)}{(\alpha + 1)}, \frac{(\beta - 1)}{(\beta + 1)}

Ans: Given polynomial equation x2 – 2x + 3 = 0

Comparing with standard polynomial, ax2 + b x + c = 0, we get,

a =  1, b = – 2, c = 3

Since, its given that the roots of the polynomial be α and β.

and we know that sum of roots (α + β) =  \frac{- b}{a}

\therefore   α + β =  \frac{- (- 2)}{1} = 2  …………… (i)

Also, we know that the product of the roots (α x β) = \frac{c}{a}

\therefore α . β = \frac{3}{1} = 3 …………. (ii)

Next, Let’s find the polynomials:

(1) Polynomial for roots (𝛼 + 2, 𝛽 + 2):

∵ Sum of the zeroes of new polynomial = (α + 2) + (β + 2) = (α + β) + 4

By transferring values from equations (i), we get:

∴ Sum of the zeroes of new polynomial = (2) + 4 = 6

Next, Product of the zeroes of new polynomial = (α + 2)(β + 2)

= αβ + 2α + 2β + 4

= αβ + 2(α + β) + 4

∴ Product of the zeroes of new polynomial = (3) + 2 (2) + 4 = 11

Since, quadratic polynomial f(x) = x2 – (sum of the zeroes)x + (product of the zeroes)
= x2 – (6) x + (11)
Hence, the required quadratic polynomial is f(x) = x2 – 6x + 11

(2) Polynomial for roots (\frac{(\alpha - 1)}{(\alpha + 1)}, \frac{(\beta - 1)}{(\beta + 1)})

∵ Sum of the zeroes of new polynomial = \frac{(\alpha - 1)}{(\alpha + 1)} + \frac{(\beta-1)}{(\beta+1)}

= \frac{(\alpha - 1)(\beta + 1) + (\beta- 1)(\alpha + 1)}{(\alpha + 1)(\beta + 1)}

= \frac{(\alpha\beta + \alpha - \beta -1) + (\alpha\beta - \alpha + \beta -1)}{(\alpha\beta + \alpha + \beta +1)}

= \frac{(2\alpha\beta - 2)}{(\alpha\beta + (\alpha + \beta) +1)}

By transferring values from equations (i) and (ii), we get:

∴ Sum of the zeroes of new polynomial = \frac{(2 (3) - 2)}{((3) + (2) +1)} = \frac{4}{6}

∴ Sum of the zeroes of new polynomial = \frac{2}{3}

Next, Product of the zeroes of new polynomial = \frac{(\alpha-1)}{(\alpha+1)} \times \frac{(\beta-1)}{(\beta+1)}

= \frac{(\alpha - 1)(\beta - 1)}{(\alpha + 1)(\beta + 1)}

= \frac{(\alpha\beta - \alpha - \beta + 1)}{(\alpha\beta + \alpha + \beta +1)}

= \frac{(\alpha\beta - (\alpha + \beta) +1)}{(\alpha\beta + (\alpha + \beta) +1)}

By transferring values from equations (i) and (ii), we get:

Product of the zeroes of new polynomial = \frac{((3) - (2) + 1)}{((3) + (2) +1)} = \frac{2}{6}

∴ Product of the zeroes of new polynomial = \frac{1}{3}  

Since, quadratic polynomial f(x) = x2 – (sum of the zeroes)x + (product of the zeroes)

= x2 \frac{2}{3} x + \frac{1}{3}

Hence, the required quadratic polynomial is f(x) = x2 \frac{2}{3} x + \frac{1}{3}

Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top