$\lim_{x\to b}\left(\frac{\tan\left(x\right)-\tan\left(b\right)}{x-b}\right)$

$tan^2\theta\:-sin^2\theta\:=tan^2\theta\:\:sin^2\theta\:$

$x-6>21-8x$

$x^2+20x->0$

$\left(a^2-\frac{1}{b^2}\right)^n.\left(a-\frac{1}{b}\right)^{-2n}$

$100x-60x+25$

$\frac{1}{5}\cdot\frac{\frac{1}{2}x}{x^2-1}$