摘要或動機

Refer to Figure 1. Suppose ABCD is a trapezoid and

. Passing the intersection
M of

and

we construct a parallel line intersecting

and


at E and F, respectively. We obtain that
, and then we can generalize
the result.



如(圖一)，若ABCD為梯形且，過
和交點M 分別作平行線交、
於E 、F ，可得
的關係，再加以推廣。