Find the value of $cos 120^{\circ}$

- \frac{1}{2}

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- \frac{1}{3}

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- \frac{1}{5}

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- \frac{1}{4}

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Solution

The correct option is B $- \frac{1}{2}$
$= cos 120^{o} = cos (90 + 30)$
$= - sin 30^{0}$
$= \frac{- 1}{2}$

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