published on: 2015-05-26 22:43:06
▲= b² - 4.a.c
i-can-feels.tumblr.com/post/119934823958/
i-can-feels.tumblr.com/post/120115683553/
i-can-feels.tumblr.com/post/120115944928/
i-can-feels.tumblr.com/post/120604500213/
i-can-feels.tumblr.com/post/120604523868/