Thread:Cdragon13/@comment-24786053-20140516110209/@comment-24908251-20140516113707

Here is a proof http://img2.wikia.nocookie.net/__cb20140516113432/khanacademy/images/5/5b/Proof.jpg

So Cdragon http://khanacademy.wikia.com/wiki/File:Rule82.jpg :1