When you square a number, whether it's positive or negative, the square is always positive. That is, a2 is positive whether a is positive or negative. Examples:
12 = 1 x 1 = 1
(-1)2 = (-1) x (-1) = 1
52 = 5 x 5 = 25
(-5)2 = (-5) x (-5) = 25
Since the answer is always positive, you don't need the absolute value signs: |a2| = a2.