Khan/khan-exercises — Issue #8892: Quadratic equation - how did you get the last step?
Author: KhanBugz
Created: 2011-12-17 19:30:13+00:00
State: open
Labels: hard, ie8, ie9, win7

how did the -3 before th eplus minus sign turn into a -1?

[quadratic_equation.html?seed=119&problem=0](http://sandcastle.khanacademy.org/media/castles/Khan:master/exercises/quadratic_equation.html?seed=119&problem=0&debug)

[Answer timeline](http://sandcastle.khanacademy.org/media/castles/Khan:master/exercises/quadratic_equation.html?seed=119&problem=0&debug&activity=%5B%5B%22incorrect-activity%22%2C%22%5C%22None%20of%20the%20above.%5C%22%22%2C114%5D%2C%5B%22incorrect-activity%22%2C%22%5C%22%3CCODE%20style%3D%5C%5C%5C%22DISPLAY%3A%20none%5C%5C%5C%22%20type%3D%5C%5C%5C%22math%2Ftex%5C%5C%5C%22%3Ex%20%3D-2%2C%5C%5C%5C%5Cfrac%7B4%7D%7B7%7D%3C%2FCODE%3E%5C%22%22%2C103%5D%2C%5B%22incorrect-activity%22%2C%22%5C%22%3CCODE%20style%3D%5C%5C%5C%22DISPLAY%3A%20none%5C%5C%5C%22%20type%3D%5C%5C%5C%22math%2Ftex%5C%5C%5C%22%3Ex%20%3D%5C%5C%5C%5Cfrac%7B5%20%5C%5C%5C%5Cpm%20%5C%5C%5C%5Csqrt%7B5%7D%7D%7B-10%7D%3C%2FCODE%3E%5C%22%22%2C4%5D%2C%5B%22incorrect-activity%22%2C%22%5C%22%3CCODE%20style%3D%5C%5C%5C%22DISPLAY%3A%20none%5C%5C%5C%22%20type%3D%5C%5C%5C%22math%2Ftex%5C%5C%5C%22%3Ex%20%3D%5C%5C%5C%5Cfrac%7B-7%20%5C%5C%5C%5Cpm%20%5C%5C%5C%5Csqrt%7B89%7D%7D%7B-10%7D%3C%2FCODE%3E%5C%22%22%2C3%5D%2C%5B%22correct-activity%22%2C%22%5C%22%3CCODE%20style%3D%5C%5C%5C%22DISPLAY%3A%20none%5C%5C%5C%22%20type%3D%5C%5C%5C%22math%2Ftex%5C%5C%5C%22%3Ex%20%3D%5C%5C%5C%5Cfrac%7B-1%20%5C%5C%5C%5Cpm%20%5C%5C%5C%5Csqrt%7B21%7D%7D%7B-6%7D%3C%2FCODE%3E%5C%22%22%2C2%5D%5D)

["None of the above.","x =-2,\\frac{4}{7}","x =\\frac{5 \\pm \\sqrt{5}}{-10}","x =\\frac{-7 \\pm \\sqrt{89}}{-10}","x =\\frac{-1 \\pm \\sqrt{21}}{-6}"]

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