sinx-siny=1/3,cosx-cosy=2/3,sin(x+y)=?

问题描述:

sinx-siny=1/3,cosx-cosy=2/3,sin(x+y)=?

sinx-siny=1/3,cosx-cosy=2/3 都平方得出:sinxsiny=4/9 cosxcosy=5/18 sin²(x+y)+cos²(x+y)=1 cos(x+y)=cosxcosy-sinxsiny=3/18sin(x+y)=5√2/2或-5√2/2