$\frac{1}{\cos^{2}x}-\tan^{2}x=1$

$\lim\:_{x\to\:0}\left(\frac{x^3-x^2}{cosx-1}\right)$

$\lim_{x\to0}\left(\frac{x^2exp\left(x\right)}{\left(exp\left(x\right)-1\right)^2}\right)$

$\frac{x^2+3x}{\sqrt{3}+\sqrt{x}}$

$\tan^2x=2$

$\frac{dy}{dt}\left(4xyt-3xt+5\left(yt\right)^3=-40\right)$

$x^6-2x^3-3$