teaa 2020-07-05T05:28:11+00:00 [img]https://img.nga.178.com/attachments/mon_202007/12/-7Q5-kj4pK6T8S2t-6e.jpg.medium.jpg[/img]用向量，坐标系，正弦定理之类的来解确实不是很难。求初中平面几何做法！