$\frac{1+sin\left(u\right)}{\cos\left(u\right)}+\frac{cos\left(u\right)}{1+sin\left(u\right)}$

$28\:x\:6$

$\left(5m+6n^2\right)\left(25m^2-30mn^2+36n^4\right)$

$t\left(t\right)=\frac{1}{64}\left(20-t\left(t\right)\right)+4$

$-\left(5-6-7\right)-\left(6-6-8+9-4-6\right)$

$\lim_{x\to\infty}\left(\frac{x^2}{\ln\left(\sqrt[2]{x}\right)}\right)$

$\lim_{x\to\infty}\left(4\cdot\sqrt{x}\right)$