Hi, Apologies for the trivialness of the question, but I'm not so great at this. I was wondering why the square root of a real number is positive. Why is sqrt(9) = 3, and not -3 as well, since (-3)² would give 9. Is it just a condition you set, that the function values must be positive? At least I thought it was, googling for it produces sites that tell the opposite, such as this one: http://thesaurus.maths.org/mmkb/entry.html?action=entryByConcept&id=1015 [Broken]. Are they wrong?