cosy=cos[(x+y)/2-(x-y)/2]=cos(x+y)/2cos(x-y)/2+sin(x+y)/2sin(x-y)/2
sinx+cosy=cos(x-y)/2[sin(x+y)/2+cos(x+y)/2]+sin(x-y)/2[sin(x+y)/2+cos(x+y)/2]=[sin(x+y)/2+cos(x+y)/2][sin(x-y)/2+cos(x-y)/2]
匿名回答于2021-03-16 01:32:18
