cosx+cosy=2cos((x+y)/2)*cos((x-y)/2),cos(x+y)=2[cos((x+y)/2)]^2-1cosX+cosy-cos(x+y)=3/2可以变为2cos((x+y)/2)*cos((x-y)/2)-2[cos((x+y)/2)]^2+1=3/2整理为4[cos((x+y)/2)]^2-4cos((x+y)/2)*cos((x-y)/2)+1=0...