证明：
sin（2x+y)/sinx-2cos(x+y)
=[sin（2x+y)-2cos(x+y)*sinx]/sinx
={sin（2x+y)-[sin（2x+y）-siny]}/sinx
=siny/sinx
得证
求证sin（2x+y)/sinx-2cos(x+y)=siny/sinx
1个回答
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