published on: 2015-05-24 21:50:20
i-can-feels.tumblr.com/post/119784657558/
i-can-feels.tumblr.com/post/119784774083/
i-can-feels.tumblr.com/post/119933432078/
▲= b² - 4.a.c
i-can-feels.tumblr.com/post/119934823958/
i-can-feels.tumblr.com/post/119972075228/