cos(x+y)-sin(x+2y)cos(x+y)−sin(x+2y)
=cosxcosy-sinxsiny-sinxcos2y-cosxsin2y=cosxcosy−sinxsiny−sinxcos2y−cosxsin2y
=cosxcosy-sinxsiny-sinx(2cos^2y-1)-2cosxsinycosy=cosxcosy−sinxsiny−sinx(2cos2y−1)−2cosxsinycosy
=cosxcosy-sinxsiny-2sinxcos^2y+sinx-2cosxsinycosy=cosxcosy−sinxsiny−2sinxcos2y+sinx−2cosxsinycosy