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9Ď13 13ST2coSCOScoS+ COS01313 |
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Answer» 2cos π/13 cos 9π/13+ cos 3π/13 +cos 5π/13 =cos 10 π/13 +cos 8 π/13 +cos 3π/13 +cos 5π/13 =cos 10 π/13 +cos 3π/13 +cos 8π/13 +cos 5π/13 =2 cos π/2 .cos 7 π/26 +2 cos π/2 .cos 3 π /26 =2 (0)cos 7 π /26 + 2(0) cos 3π/26 =0 =R.H.S. |
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