SSC CHSL Model Paper 13

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Question : 64 of 100

Marks: +1, -0

If

x+1/x=√5

, then

x^3+1/x^3

is equal to:

$3√5$
$4√5$
$2√5$
$5√5$

Solution:

x+1/x=√5

(x+1/x)^3=(√5)^3

x^3+1/x^3+3×x

×1/x(x+1/x)=5√5

⇒x^3+1/x^3+3√5=5√5

⇒x^3+1/x^3=5√5-3√5=2√5

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