$\lim_{x\to\infty}\left(\frac{x+3}{x^2-9}\right)$

$\frac{s^4+81}{s\left(s^2+9\right)^2}$

$10^{log50-log5}$

$5\left(x+10\right)-25=5x+25$

$f ( t ) = \frac { 9 - t ^ { 2 } } { t - 3 }$

$k^2\:3k^0$

$\frac{cos\:\left(a\right)+sen\:\left(a\right)}{cos\:\left(a\right)\:sen\:\left(a\right)}$