Khan/khan-exercises — Issue #12796: Factoring difference of squares 2 - Factor out the 81?
Author: KhanBugz
Created: 2012-02-01 14:07:24+00:00
State: open
Labels: ie8, win7, wrong-or-unclear

Reporter: ajsoley@hotmail.com

Factoring 81x^2−81 as 81(x+1)(x-1) was graded as incorrect. It's not.

[factoring_difference_of_squares_2.html?seed=0&problem=0](http://sandcastle.khanacademy.org/media/castles/Khan:master/exercises/factoring_difference_of_squares_2.html?seed=0&problem=0&debug)

[Answer timeline](http://sandcastle.khanacademy.org/media/castles/Khan:master/exercises/factoring_difference_of_squares_2.html?seed=0&problem=0&debug&activity=%5B%5B%22incorrect-activity%22%2C%22%5B%5C%229(x-1\)(x%2B1\)%5C%22%5D%22%2C9%5D%2C%5B%22incorrect-activity%22%2C%22%5B%5C%2281(x-1\)(x%2B1\)%5C%22%5D%22%2C49%5D%2C%5B%22incorrect-activity%22%2C%22%5B%5C%2281(x-1\)(x%2B1\)%5C%22%5D%22%2C26%5D%2C%5B%22correct-activity%22%2C%22%5B%5C%22(9x-9\)(9x%2B9\)%5C%22%5D%22%2C10%5D%5D)

[["9(x-1)(x+1)"],["81(x-1)(x+1)"],["81(x-1)(x+1)"],["(9x-9)(9x+9)"]]

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