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#