Khan/khan-exercises — Issue #6948: Parabola intuition 3 - Wrong calculation for Parabola
Author: KhanBugz
Created: 2011-11-23 02:25:00+00:00
State: open
Labels: chrome, wrong-or-unclear

Reporter: tiwoc@arcor.de

Focus is (1, 3/8), Directrix is y=5/8.

The solution should be y-1/2 = -2*(x-1)^2.

However, the value for y_1 is not accepted. In the error text, it says: "So x_1 = 1. And y_1 = (3/8+5/8)/2 = 1". This is clearly wrong as (3/8+5/8)/2 = 1/2.

[parabola_intuition_3.html?seed=174&problem=0](http://sandcastle.khanacademy.org/media/castles/Khan:master/exercises/parabola_intuition_3.html?seed=174&problem=0&debug)

[Answer timeline](http://sandcastle.khanacademy.org/media/castles/Khan:master/exercises/parabola_intuition_3.html?seed=174&problem=0&debug&activity=%5B%5B%22incorrect-activity%22%2C%22%5B%5C%221%2F2%5C%22%2C%5C%22-2%5C%22%2C%5C%221%5C%22%2C%5C%220.5%5C%22%2C%5C%220.375%5C%22%2C%5C%220.625%5C%22%5D%22%2C68%5D%2C%5B%22hint-activity%22%2C%220%22%2C0%5D%2C%5B%22hint-activity%22%2C%220%22%2C0%5D%2C%5B%22hint-activity%22%2C%220%22%2C0%5D%2C%5B%22hint-activity%22%2C%220%22%2C0%5D%2C%5B%22hint-activity%22%2C%220%22%2C0%5D%2C%5B%22hint-activity%22%2C%220%22%2C0%5D%2C%5B%22hint-activity%22%2C%220%22%2C0%5D%2C%5B%22hint-activity%22%2C%220%22%2C0%5D%5D)

[["1/2","-2","1","0.5","0.375","0.625"]]

Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/535.1 (KHTML, like Gecko) Ubuntu/11.10 Chromium/14.0.835.202 Chrome/14.0.835.202 Safari/535.1

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