Evaluate $ \cos 240^{\circ} $.

Given:

$cos\ 240^o$.

To do:

We have to evaluate $cos\ 240^o$.

Solution:
We know that,

$cos\ (180+x)=-cos\ x$ and

$cos\ 60^o=\frac{1}{2}$

Therefore,

$cos\ 240^o=cos\ (180+60)^o$

$=-cos\ 60^o$

$=-\frac{1}{2}$

Therefore, $cos\ 240^o=-\frac{1}{2}$.

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Updated on: 10-Oct-2022

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