S梯形ABCD=1/2* (a+b)^2
= 1/2*(a^2+2ab+b^2), ①
又S梯形ABCD=S△AED+S△EBC+S△CED
= 1/2*(ab+ ba+ c^2)
=1/2 *(2ab+c^2). ②
比较以上二式,便得
a^2+b^2=c^2.
S梯形ABCD=1/2* (a+b)^2
= 1/2*(a^2+2ab+b^2), ①
又S梯形ABCD=S△AED+S△EBC+S△CED
= 1/2*(ab+ ba+ c^2)
=1/2 *(2ab+c^2). ②
比较以上二式,便得
a^2+b^2=c^2.