Avoid misleading answer

Reviewers: eater

CC: alpert

Differential Revision: http://phabricator.khanacademy.org/D7026
Correctly avoid misleading answer
Merge branch 'master' of https://github.com/Khan/khan-exercises
Change hints to avoid using trigonometry

Reviewers: eater

Reviewed By: eater

CC: justin, alpert

Differential Revision: http://phabricator.khanacademy.org/D6849