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Question #ebf14

1 Answer

Jun 3, 2017

The answer is $=-79/81=-0.975$

Explanation:

We need

$cos4theta=2cos^2 2theta-1$

As,

$cos2theta=1/9$

$cos4theta=2*(1/9)^2-1=2/81-1=-79/81=-0.975$

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