$\int-9^{-2x}dx$

$\lim_{t\to0}\left(\frac{\cos\left(at\right)-\cos\left(bt\right)}{t}\right)$

$-a^2-a^2$

$\frac{dy}{dx}=4e^2$

$2tan^22x-\frac{2}{cos^22x}$

$\frac{\sqrt{3}}{6}\arctan\left(\frac{\sqrt{3}}{2}\tan\left(x\right)\right)$

$x\left(t\right)=\frac{t}{k}-\frac{1}{k^2}+ce^{-kt}$