So for this you will be doing proportions. And in this case, the proportion is [tex] \frac{9}{x} =\frac{x}{12} [/tex]
Firstly, you'll need to cross multiply. Your equation will look like this: [tex] 108=x^2 [/tex]
Finally, square root each side and your answer will be [tex] \sqrt{108}=x [/tex]. However this can be simplified.
[tex] \sqrt{108} =\sqrt{18*6}=\sqrt{9*2*3*2}=2\sqrt{3*3*3} =3*2\sqrt{3} =6\sqrt{3} [/tex]
In short, your answer is [tex] 6\sqrt{3} [/tex]
