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证明: sin7x+sinx/sin5x+sin3x=4Cos^2 x%3

证明 分子 sin(4x+3x)+sin(4x-3x) =sin4xcos3x+cos4xsin4x+sin4xcos3x-cos4xsin4x =2sin4xcos3x 分母 sin(4x+x)+sin(4x-x) =sin4xcosx+cos4xsinx+sin4xcosx-cos4xsinx =2sin4xcosx 左=(2sin4xcos3x)/(2sin4xcosx)=cos3x/cosx,其中 ...

sin^2xsin3x =0.5(1-cos4x)sin3x =0.5 sin3x-0.5sin3xcos4x =0.5sin3x-0.25 (sin7x-sinx) I= -1/6 cos3x + 1/28 cos7x- 1/4 cosx +C

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