published on: 2015-05-24 19:17:10
i-can-feels.tumblr.com/post/119784131108/
i-can-feels.tumblr.com/post/119784268098/
i-can-feels.tumblr.com/post/119784774083/
i-can-feels.tumblr.com/post/119795922098/
i-can-feels.tumblr.com/post/119933432078/
▲= b² - 4.a.c