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Question

The value of cos 12+cos 84+cos 132+cos 156 is

A
1
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B
12
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C
12
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D
14
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Solution

The correct option is D 12

cos12°+cos84°+cos156°+cos132°
=(cos12°+cos132°)+(cos84°+cos156°)
=2cos72°cos60°+2cos120°cos36°
=cos72°cos36°=sin18°cos36°
=1/2

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