$\frac{dy}{dx}\sqrt{3+\sqrt{7x}}$

$x^2-x+1>0$

$\lim_{x\to\pi}\left(\frac{\left(\pi-x\right)\cos\left(x-\frac{3\pi}{2}\right)}{1-\sec\left(x-\pi\right)}\right)$

$\frac { 2 n - 2 n } { 2 n }$

$\lim_{x\to0}\:\frac{\tan\left(x\right)}{x}x\cos\left(x\right)$

$\lim_{x\to\infty}\sqrt{x^2+3}$

$y=2x^2-6x;\:x=-6$