化简sin(x+y)sinx+cos(x+y)cosx等于?

问题描述:

化简sin(x+y)sinx+cos(x+y)cosx等于?

sin(x+y)sinx+cos(x+y)cosx=
(sinxcosy+sinycosx)sinx+(cosxcosy-sinxsiny)cosx=
(sinx)^2 *cosy+(cosx)^2*cosy=
(sinx平方+cosx平方)*cosy=
1*cosy=cosy