published on: 2015-05-26 13:03:25
i-can-feels.tumblr.com/post/119933432078/
▲= b² - 4.a.c
i-can-feels.tumblr.com/post/119972075228/
i-can-feels.tumblr.com/post/120115683553/
i-can-feels.tumblr.com/post/120115944928/
i-can-feels.tumblr.com/post/120604500213/