find the value cos12°+cos132° +cos84°+cos156°.
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Cos 12 + Cos 84 + Cos 132 + Cos 156 (Cos 12 + Cos 156) + (Cos 132 + Cos 84) 2Cos(84)cos72 + 2cos108cos24 2Cos(84)cos72 - 2cos72cos24 2cos72(Cos84-cos24) 2cos72 x 2 sin 54 sin30 4 sin18 cos36 sin 30 4((âˆڑ5-1/4) ( 1 + âˆڑ5)/4 (1/2) = 4 x 4/16 x آ½ =1/2
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