$\cot\left(x-y\right)=\frac{1}{\tan\left(x-y\right)}$

$\lim_{x\to3}\left(\frac{x^2-9}{\sqrt{3x}-x^2}\right)$

$-3+\left(+7\right)-\left(+8\right)-\left(-2\right)$

$\lim_{x\to\infty}x\left(\sqrt{x^2+1}-\sqrt{x^2-1}\right)$

$\frac{x^3-46x+22}{x+7}$

$\left(5x-2b\right).\:\left(5x+2b\right)$

$\left(\frac{x}{9}^{12}-\frac{7}{6}\right)^3$