$latex x^{2}-3^{r-9^t}$
$latex \dfrac {x^{2}-3^{r-9^t}}{2}$
http://www.artofproblemsolving.com/LaTeX/AoPS_L_GuideLay.php#layout
$latex x^{2}-3^{r-9^t}$
$latex \dfrac {x^{2}-3^{r-9^t}}{2}$
http://www.artofproblemsolving.com/LaTeX/AoPS_L_GuideLay.php#layout