证明 [sin(2x+y)/sinx]-2cos(x+y)=siny/sinx
证明 [sin(2x+y)/sinx]-2cos(x+y)=siny/sinx
数学人气：297 ℃时间：2020-01-27 22:50:32
优质解答
[sin(2x+y)/sinx]-2cos(x+y)={[sin(x+y)cosx+cos(x+y)sinx]/sinx}-2cos(x+y)={[sin(x+y)cosx+cos(x+y)sinx-2cos(x+y)sinx]/sinx=[sin(x+y)cosx-cos(x+y)sinx]/sinx=sin(x+y-x)/sinx=siny/sinx
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