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Show that costhetacos(60^(@)+theta)cos(6...

Show that `costhetacos(60^(@)+theta)cos(60^(@)-theta)=1/4 cos3theta ` and hence deduce that `"cos"pi/9"cos"(3pi)/9"cos"(5pi)/9"cos"(7pi)/9=1/16` (T.S.MAY-2016)

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