Question

If one root of a equation is 2 +V5, then the quadratic equation is :
(a) x' + 4x – 1=0 (b) x² - 4x -1 = 0 (c) x2 + 4x + 1 =0
(d) x - 4x + 1 = 0
Lugh the​

Answer 1

Answer:

let alpha and beta be the roots of given quadratic equation

alpha=2+root5

beta=2-root5 (by rationalisation)

alpha+beta=4

alpha.beta=-1

now new equation =x^2-(alpa+beta)x+alpha.beta

=x^2-4x-1=0

hence answer b is correct

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