If 4 x^{2}-6 x+1=0, then the value of 8 x^{3}+ (8 x^{3} )^{-1} is :

SSC CGL 10 Jun 2019 Shift 1 Paper

Question : 52 of 100

Marks: +1, -0

4 x^{2}-6 x+1=0,

then the value of

8 x^{3}+

\ (8 x^{3}\ )^{-1}

is :

Solution:

4 x^{2}-6 x+1=0

\⇒2 x-3+\ {1}/{2 x}=0

\⇒2 x+\ {1}/{2 x}=3

Now,

8 x^{3}+\ {1}/{8 x^{3}}=(3)^{3}-3(3)

=27-9=18

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