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Prove the following : Express 4cosA.cosB.cosC as the sum of four cosines. |
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Answer» SOLUTION :4cosAcosBcosC = 2(2cosAcosB)COSC = 2[COS(A+B)+cos(A-B)]cosC = 2COS(A+B)cosC+2cos(A-B)cosC cos(A+B+C)+cos(A+B-C)+cos(A-B+C)+cos(A-B-C) |
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