2cos(x+y)cosx-cos(2x+y)化简
题目
2cos(x+y)cosx-cos(2x+y)化简
答案
2cos(x+y)cosx-cos(2x+y)
=2cos(x+y)cosx-cos[(x+y)+x]
=2cos(x+y)cosx-cos(x+y)cosx+sin(x+y)sinx
=cos(x+y)cosx+sin(x+y)sinx
=cos[(x+y)-x]
=cosy
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