Question 477947
Area = {{{4x^2 + 12x + 9 = (2x + 3)^2}}}.

==> side of square is 2x+3.  


(Some would argue that the length of the side would be |2x+3|, but this would be erroneous, since 2x + 3 has to be positive, and so {{{sqrt((2x+3)^2) = abs(2x+3) = 2x+3}}}.)