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Prove that: 2cOS COSCOScos02cosTS⌠131313 |
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Answer» 2cos pi/13 cos 9pi/13+ cos 3pi/13 +cos 5pi/13 =cos 10 pi/13 +cos 8 pi/13 +cos 3pi/13 +cos 5pi/13 =cos 10 pi/13 +cos 3pi/13 +cos 8pi/13 +cos 5pi/13 =2 cos pi/2 .cos 7 pi/26 +2 cos pi/2 .cos 3 pi /26 =2 (0)cos 7 pi /26 + 2(0) cos 3pi/26 =0 =R.H.S. |
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