How do you find the exact value of $cos(-30)$ ?

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Answer 1 · 2018-03-17T04:55:44

$color(brown)(cos (-30) = cos 30 = cos (pi/6) = sqrt3 / 2 = 0.866$

To get exact value of $cos(-30)$

$cos (-30)$ is in IV quadrant where only cos and sec are positive.

Hence $cos(-30) = cos 30 = cos (pi/6)$

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From the above table,

$color(brown)(cos (-30) = cos 30 = cos (pi/6) = sqrt3 / 2 = 0.866$

How do you find the exact value of cos(-30)cos(-30)?