Elementary Algebra

{$-\frac{2}{3}$}
Using the rules for factoring trinomials and setting the factors equal to zero, we obtain: $9x^{2}+12x+4=0$ $9x^{2}+6x+6x+4=0$ $3x(3x+2)+2(3x+2)=0$ $(3x+2)(3x+2)=0$ $(3x+2)=0$ or $(3x+2)=0$ $x=-\frac{2}{3}$ Therefore, the solution set is {$-\frac{2}{3}$}.