SSC CGL Tier II 21 Sep 2014 Paper

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Question : 20 of 100

Marks: +1, -0

If

3 x+ {3}/{x}=1

then

x^{3}+ {1}/{x^{3}}+1

is

0
$1 /27$
$5/ 27$
$28/ 27$

Solution:

(2)

3 x+ {3}/{x}=1

⇒ x+ {1}/{x}= {1}/{3}

On cubing both sides,

x^{3}+ {1}/{x^{3}}+3\ (x+ {1}/{x} )= {1}/{27}

⇒ x^{3}+ {1}/{x^{3}}+3 ×{1}/{3}= {1}/{27}

⇒ x^{3}+ {1}/{x^{3}}+1= {1}/{27}

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