已知sin(x+2y)=3sinx,求tan(x+y)*coty

问题描述:

已知sin(x+2y)=3sinx,求tan(x+y)*coty

sin(x+2y)=3sinx ,sin[(x+y)+y]=3sin[(x+y)-y] ,sin(x+y)cos(y)+cos(x+y)sin(y)=3[sin(x+y)cos(y)-cos(x+y)sin(y)] ,sin(x+y)cos(y)=2cos(x+y)sin(y) ,tan(x+y)*coty=2