Square root of 9a to the 2nd power if a<0

Question

Please hurry I need this answer very quickly.

Answer 1

generally if you square something, then take the square root, you go back to where you started, 9a<0

but "square root" unless specified otherwise, means the positive square root. So you square 9a to get 81a^2

then take the positive square root = -9a, since a<0, then -9a >0

answer: -9a

another way to write the solution is: absolute value of -9a = l-9al

which = -9a since a<0, but would have = 9a had a been positive