sinx+siny=1/3,cosx-cosy=1/5
两式分别平方得
sin²x+sin²y+2sinxsiny=1/9
cos²x+cos²y-2cosxcosy=1/25
相加得
1+1+2sinxsiny-2cosxcosy=1/9+1/25=34/225
2cosxcosy-2sinxsiny=2-34/225
cosxcosy-sinxsiny=1-17/225=208/225
∴cos(x+y)=208/225请问sin(x-y)=?感觉题目有误，我想了半天也算不出来，不好意思哈