$\underset{x\to 2}{\lim }\frac{3^x+3^{3-x}-12}{3^{\frac{-x}{2}}-3^{1-x}}$is equal to _______.

$\underset{x\to 2}{\lim }\frac{3^x+3^{3-x}-12}{3^{-{\displaystyle \frac{x}{2}}}-3^{1-x}}=\underset{x\to 2}{\lim }\frac{3^{2x}-{12.3}^x+27}{3^{{\displaystyle \frac{x}{2}}}-3}$

                                $=\underset{x\to 2}{\lim }\frac{\left(3^x-9\right)\left(3^x-3\right)}{\left(3^{{\displaystyle \frac{x}{2}}}-3\right)}$

                                $=\underset{x\to 2}{\lim }\frac{\left(3^{{\displaystyle \frac{x}{2}}}+3\right)\left(3^{{\displaystyle \frac{x}{2}}}-3\right)\left(3^x-3\right)}{\left(3^{{\displaystyle \frac{x}{2}}}-3\right)}$

                                $=36$

(cancel out the common factor and then plug in x=2)