摘要
本文利用射影几何的理论，采用了四种不同的方法，对蝴蝶定理进行了证明，并给出了仿射的和射影的若干推广．
In this paper, by using projective geometry theory,we have separately proved Butterfly Theorem with four different methodes, ang have extended it to affine and projective geometry.
关键词
蝴蝶定理
正交变换
射影性质
交比
对合
Butterfly Theorem, Orthogonal transformation, projective property, cross ratio, involution
