问题标题:
为什么sin(x+y)-sinx=2cos(x+y/2)siny/2
问题描述:
为什么sin(x+y)-sinx=2cos(x+y/2)siny/2
洪晓斌回答:
x+y=x+y/2+y/2x=x+y/2-y/2sin(x+y)=sin(x+y/2+y/2)=sin(x+y/2)cosy/2+cos(x+y/2)siny/2sinx=sin(x+y/2)cosy/2-cos(x+y/2)siny/2所以sin(x+y)-sinx=sin(x+y/2)cosy/2+cos(x+y/2)siny/2-[sin(x+y/2)cosy/2-cos(x+y...
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