GMAT Math

ya the square root of a nos is always +ve

This is coming out straight from the OG 11th Edition Quantitative Review book (written by GMAC themselves):

"every positive n has 2 square roots, one positive and one negative. but √n denotes the positive number whose square is n.
E.g. √9 denotes 3
The 2 square roots of 9 are √9=3, and -√9=-3"

hope this clarifies.

Best.
II

solving for x in x= root(M) is always positive
However solving for x in x^2 = M means x takes on both values of root(M)
This is math conventions