published on: 2015-05-24 19:18:48
i-can-feels.tumblr.com/post/119784268098/
i-can-feels.tumblr.com/post/119784657558/
i-can-feels.tumblr.com/post/119795922098/
i-can-feels.tumblr.com/post/119933432078/
▲= b² - 4.a.c
i-can-feels.tumblr.com/post/119934823958/