三角函数 1.解x,2（cosx）平方+3sinx=3 2.证明（sinx-sin2x+sin3x）/(cosx-cos2x+cos3x)=tan2x

2（cosx）平方+3sinx=3
2(1-sinx平方）+3sinx=3
2sinx平方-3sinx+1=0
sinx=1,sinx=1/2
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（sinx-sin2x+sin3x）/(cosx-cos2x+cos3x)
=（sinx+sin3x-sin2x）/(cosx+cos3x-cos2x)
=(2sin2xcosx-sin2x)/(2cos2xcosx-cos2x)
=sin2x/cos2x
=tan2x还有一题.....sin5x-sin3x+sinx=osin5x+sinx-sin3x=o2sin3xcosx-sin3x=0sin3x(2cosx-1)=0sin3x=0,x=2kπcosx=1/2x=2kπ±π/3