Take any convex quadrilateral ABCD, with diagonals AC and BD. Pick E so ABCE is a parallelogram. Prove that AB²+BC²+CD²+DA²= AC²+BD²+DE².

Given the same quadrilateral, let P and Q be the midpoints of AC and BD. Now prove that AB²+BC²+CD²+DA²= AC²+BD²+4PQ².

(In reply to 2nd proof w/ a cheat by nikki)

hahah ^^nice job nikki~ =)

i'm working on the first proof...soo rusty on this kinda math...=_=

Posted by Amon on 2005-05-05 00:36:33