$x \cdot 3^x+C$

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

$x^2 3^x+C$

$\frac{3^x}{x}+C$

$-\sec ^2\left(\frac{\pi}{4}-x\right)+C$

$-\log \left|\sec \left(\frac{\pi}{4}-x\right)\right|+C$

$\sec ^2\left(\frac{\pi}{4}-x\right)+C$

$\log \left|\sec \left(\frac{\pi}{4}-x\right)\right|+C$

$\frac{x^2}{4}\left(\pi-\cos ^{-1} x^2\right)+\frac{1}{4} \sqrt{1-x^2}+C$

$\frac{x^2}{4}\left(\pi-\cos ^{-1} x^2\right)+\frac{1}{4} \sqrt{1-x^4}+C$

$\frac{x^2}{4}\left(\pi+\cos ^{-1} x^2\right)-\frac{1}{4} \sqrt{1-x^4}+C$

$\frac{x^2}{4}\left(\pi+\cos ^{-1} x^2\right)-\frac{1}{4} \sqrt{1-x^2}+C$

$\frac{1}{2+\tan x}+C$

$-\frac{1}{2 \tan x+1}+C$

$\frac{\cos x}{\cos x+2 \sin x}+C$

$-\frac{\cos x}{2 \cos x+\sin x}+C$