@[Wy121212](/space/show?uid=93483) 还是错了...
$\sin(A+B)=\sin A \cos B+\cos A\sin B$
by cqqqwq @ 2018-06-06 22:34:32
@[陈启乾](/space/show?uid=57601) 发现了....
by Chloris @ 2018-06-06 22:35:05
@[陈启乾](/space/show?uid=57601) 打错了谔谔，今天还做余弦定理来着，，，
by x_angelkawaii_x @ 2018-06-06 22:35:26
@[larryzhong](/space/show?uid=20438) 谢谢
by Chloris @ 2018-06-06 22:37:01
@[larryzhong](/space/show?uid=20438) 是高中课本吗
by Chloris @ 2018-06-06 22:37:24
用向量证明
by 文文殿下 @ 2018-06-06 22:41:18
@[文文殿下](/space/show?uid=64618) 如何用向量证明？
by Chloris @ 2018-06-06 22:42:43
@[Chloristendika](/space/show?uid=76527)
给你个解法吧，不要再问了，，，
先画个单位圆，设单位向量a=(cosx,sinx),b=(cos(90-y),sin(90-y)),则<a,b>=90-(x+y)
ab=|a|*|b|*cos<a,b>=cos(90-(x+y))=sin(x+y)=cosxsiny+sinxcosy
by x_angelkawaii_x @ 2018-06-06 22:49:59
@[Wy121212](/space/show?uid=93483) %%%大佬，可能我还需要跑去问一下数学老师
by Chloris @ 2018-06-06 22:51:20
@[Chloristendika](/space/show?uid=76527) 对了，那个恶心题还用到三角函数呃，，，
by x_angelkawaii_x @ 2018-06-06 22:53:52