If alpha and beta are zeroes of a quadratic polynomial Fx = 2x square ...
Problem:
If alpha and beta are zeroes of a quadratic polynomial Fx = 2x square -5x 7. Find a polynomial who's zeroes are 2 alpha 3 beta and 3 alpha 2 beta? Explain in details.
Solution:
Given quadratic polynomial is Fx = 2x^2 - 5x + 7. Let alpha and beta be zeroes of Fx.
Sum and Product of roots
Sum of roots = alpha + beta = (-b/a) = -(-5)/2 = 5/2
Product of roots = alpha * beta = c/a = 7/2
Polynomial with roots 2alpha and 3beta
Let Gx be a polynomial whose zeroes are 2alpha and 3beta.
Then, Gx = (x - 2alpha) (x - 3beta)
Expanding, Gx = x^2 - (2alpha + 3beta) x + 6alpha beta
Substituting the values of alpha and beta, we get:
Gx = x^2 - 5x + 21/2
Polynomial with roots 3alpha and 2beta
Let Hx be a polynomial whose zeroes are 3alpha and 2beta.
Then, Hx = (x - 3alpha) (x - 2beta)
Expanding, Hx = x^2 - (3alpha + 2beta) x + 6alpha beta
Substituting the values of alpha and beta, we get:
Hx = x^2 - 13x/2 + 21/2
Final polynomial
Let Jx be the polynomial whose zeroes are 2alpha, 3beta, 3alpha and 2beta.
Then, Jx = Gx * Hx
Expanding, Jx = (x^2 - 5x + 21/2) (x^2 - 13x/2 + 21/2)
On simplifying, we get:
Jx = 2x^4 - 18x^3 + 61x^2 - 87x + 220/4
Jx = x^4 - 9x^3 + 61/2 x^2 - 87/2 x + 55/2