Khan/khan-exercises — pull request #19394 by beneater (2012-04-13 18:10:51+00:00)
Title: Revive square and cube root exercise and split it up

I always wondered why we didn't have exercises on square roots. It turns out we do! They were just never added to the knowledge map. I've split this into two exercises to provide more granularity and tweaked the hints slightly.