Khan/khan-exercises — Issue #6992: Inverse trig functions - won't accept 0 pi as answer
Author: KhanBugz
Created: 2011-11-23 21:56:08+00:00
State: open
Labels: firefox, win7, wrong-or-unclear

Reporter: john514450418@gmail.com

I entered 0 pi (my first an only answer to that specific question), it's the right answer (I checked with the hints, see below), but it won't accept it.

It might be a bug, or I might just have missed something really obvious as I'm really tired!

thanks again for the amazing work and the amazing website.

cheers!

==
What is the principal value of arctan(0)\arctan\left(0\right)?

Note: please answer in terms of radians (ex: "3/4 pi").

arctan(0)=tan−1(0)\arctan\left(0\right) = \tan^{-1}\left(0\right)

If tan−1(0)=θ\tan^{-1}\left(0\right) = \theta, then...

tan(θ)=0\tan\left( \theta \right) = 0

The range of arctan(x)\arctan\left(x\right) is [−π2,π2][ -\frac{\pi}{2}, \frac{\pi}{2} ], so we know −π2≤θ≤π2-\frac{\pi}{2} \leq \theta \leq \frac{\pi}{2}.

tan(0π)=0\tan \left( 0\pi \right) = 0

So arctan(0)=0π\arctan\left(0\right) = 0\pi.

[inverse_trig_functions.html?seed=82&problem=0](http://sandcastle.khanacademy.org/media/castles/Khan:master/exercises/inverse_trig_functions.html?seed=82&problem=0&debug)

[Answer timeline](http://sandcastle.khanacademy.org/media/castles/Khan:master/exercises/inverse_trig_functions.html?seed=82&problem=0&debug&activity=%5B%5B%22incorrect-activity%22%2C%22%5C%220%20pi%5C%22%22%2C7%5D%2C%5B%22incorrect-activity%22%2C%22%5C%220%20pi%5C%22%22%2C169%5D%2C%5B%22hint-activity%22%2C%220%22%2C76%5D%2C%5B%22hint-activity%22%2C%220%22%2C79%5D%2C%5B%22hint-activity%22%2C%220%22%2C83%5D%2C%5B%22hint-activity%22%2C%220%22%2C85%5D%2C%5B%22hint-activity%22%2C%220%22%2C101%5D%2C%5B%22hint-activity%22%2C%220%22%2C101%5D%2C%5B%22incorrect-activity%22%2C%22%5C%220%20pi%5C%22%22%2C127%5D%2C%5B%22incorrect-activity%22%2C%22%5C%220%20pi%5C%22%22%2C32%5D%2C%5B%22incorrect-activity%22%2C%22%5C%220%20pi%5C%22%22%2C348%5D%5D)

["0 pi","0 pi","0 pi","0 pi","0 pi"]

Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.2.23) Gecko/20110920 Firefox/3.6.23

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