求证sin(2x+y)/sinx-2cos(x+y)=siny/sinx

问题描述:

求证sin(2x+y)/sinx-2cos(x+y)=siny/sinx

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