Khan/khan-exercises — Issue #6738: Equation of a hyperbola - Bug... incorrect answer marked as correct
Author: KhanBugz
Created: 2011-11-20 08:30:02+00:00
State: open
Labels: firefox, other, snowleo

Reporter: michael@malione.com

The exercise gave the hyperbola equation:

(y−4)^2/81 − (x−8)^2/4 = 1

The correct answer should have been:

y = ±9(x-8)/2+4

However, I entered the answer:

y = ±9x/2-32

The scorer marked my answer as correct. Given the possibilities implied by the ± sign, these answers are NOT equivalent.

In some problems, the scorer catches this difference and marks it wrong, but in others, such as the one indicated here, it does not.

[equation_of_a_hyperbola.html?seed=57&problem=0](http://sandcastle.khanacademy.org/media/castles/Khan:master/exercises/equation_of_a_hyperbola.html?seed=57&problem=0&debug)

[Answer timeline](http://sandcastle.khanacademy.org/media/castles/Khan:master/exercises/equation_of_a_hyperbola.html?seed=57&problem=0&debug&activity=%5B%5B%22correct-activity%22%2C%22%5B%5C%229x%2F2-32%5C%22%5D%22%2C209%5D%5D)

[["9x/2-32"]]

Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:7.0.1) Gecko/20100101 Firefox/7.0.1

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