Question

square root of (x+6)^6

Answer 1

http://www.wolframalpha.com/input/?i=simplify+square+root+of+%28x%2B6%29%5E6

Answer 2

Whoops! Wolfram needs a better explanation.

\(\sqrt{(x+6)^6} = \left|(x+3)^3\right|\)

The left-hand expression is necessarily non-negative.
The right-hand expression, without the Absolute Values, is not restricted from being negative. We must restrict it with the Absolute Values.