SSC CGL 10 Jun 2019 Shift 2 Paper

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Question : 54 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}

Cubing both sides

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

=5 \√{3}-3 \√{5}=2 \√{5}

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