Changes

==Two square roots ==

==Two square roots ==

All numbers other than zero have two square roots, one positive and one negative: <ref>"Note that any positive real number has two square roots, one positive and one negative. For example, the square roots of 9 are -3 and +3, since (-3)^2==(+3)^2==9." [http://mathworld.wolfram.com/SquareRoot.html Wolfram Research] - Eric Weisstein </ref>

If <math>x^2 = y</math> then <math>x = \abs(y)</math>.  This implies that all numbers other than zero have two square roots, one positive and one negative: <ref>"Note that any positive real number has two square roots, one positive and one negative. For example, the square roots of 9 are -3 and +3, since (-3)^2==(+3)^2==9." [http://mathworld.wolfram.com/SquareRoot.html Wolfram Research] - Eric Weisstein </ref>

:<math>3 \cdot 3 = 9</math> and <math>-3 \cdot -3 = 9</math>

:<math>3 \cdot 3 = 9</math> and <math>-3 \cdot -3 = 9</math>