This problem gives you the area of a square, and asks for the length of a side. The formula for the area [tex] A [/tex] of a square, knowing the side [tex] s [/tex], is
[tex] A = s^2 [/tex]
But we are in the opposite situation: we know the area and we are looking for the side. So, we need to invert the formula above:
[tex] s = \pm\sqrt{A} [/tex]
But since the length of a side can't be negative, we choose
[tex] s = \sqrt{A} [/tex]
So, if we plug the value for the area, we have
[tex] s = \sqrt{20.25} = 4.5 [/tex]
