$\log \left(x\right)+\log \left(x-3\right)=1$

$\int_2^{\infty}\left(\frac{1}{x^2+6x+5}\right)dx$

$\int_0^{\infty}\left(\frac{1}{\sqrt{x}+x^2}\right)dx$

$\int_0^{\infty}\left(\frac{x}{1+x^3}\right)dx$

$\int_0^{\infty}\left(\frac{x}{x^3+1}\right)dx$

$\int_0^1\left(\frac{x}{1-x^2}\right)dx$

$\int_0^1\frac{dx}{\left(x+1\right)\left(x^2+1\right)}$

$\int_1^2\frac{1}{x\cdot\left(x+1\right)}dx$