SSC CHSL 6 Dec 2015 Shift 2 Paper

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Question : 115 of 200

Marks: +1, -0

If for non-zero x,

x^2-4x-1=0

the value of

x^2+1/x^2

is :

10
4
12
18

Solution:

Given :

x^2 − 4x − 1 = 0

⇒

x^2 − 1 = 4x

⇒

{x^2-1}/x=4

⇒

x-1/x=4

Squaring both sides, we get :
⇒

(x-1/x)^2=4^2

⇒

x^2+1/x^2-2(x)(1/x)=16

⇒

x^2+1/x^2=16+2=18

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