关于三角函数,
sin(x/2)cos(x/2 兀/3) cos(x/2)sin(x/2 兀/3)=sin(x x 兀/3) 请原谅我用这个东西代替圆周率……
加号呢？sinxcos(x＋兀/3)＋cosxsin(x＋兀/3)＝sin(x＋x＋兀/3)