已知cos(x-y)cosx+sin(x-y)sinx=3/5,则cosy的值为
问题描述:
已知cos(x-y)cosx+sin(x-y)sinx=3/5,则cosy的值为
答
cos(x-y)cosx+sin(x-y)sinx=cos(x-y-x)=cos(-y)=cosy=3/5
已知cos(x-y)cosx+sin(x-y)sinx=3/5,则cosy的值为
cos(x-y)cosx+sin(x-y)sinx=cos(x-y-x)=cos(-y)=cosy=3/5