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How do you evaluate $cos - 120$ $cos-120$ ?

1 Answer

Shwetank Mauria

Jun 29, 2016

$cos (- 120^{o}) = - \frac{1}{2}$ $cos(-120^o)=-1/2$

Explanation:

$cos (- 120^{o}) = {cos 120}^{o}$ $cos(-120^o)=cos120^o$

= $cos (180^{o} - 60^{o})$ $cos(180^o-60^o)$

= $- {cos 60}^{o}$ $-cos60^o$

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

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