$\frac{u^4}{u^2}-\frac{81}{9}$

$\left(2x+1\right)^2=4x$

$-\int\frac{\sin^2\left(x\right)}{\cos\left(x\right)}dx$

$t+\frac{t^2}{2}+t^2+t$

$\frac{\left(x^2\:y^3\right)^4\left(xy^4\right)^{-3}}{x^2y}$

$\frac{\sin^2\left(x\right)}{\cot^2\left(x\right)}+\sin^2\left(x\right)=\tan^2\left(x\right)$

$\lim_{x\to\infty}\:\frac{2x}{\sqrt{4x^2+1}}$