$$ \int_0^{\pi / 2} \frac{x \tan x \sec ^2 x}{\tan ^4 x+1} d x= $$

$$ \int_3^6 \frac{\sqrt{x}}{\sqrt{9-x}+\sqrt{x}} d x= $$

$$ \lim _{n \rightarrow \infty}\left[\left(1+\frac{1}{n^2}\right)\left(1+\frac{2^2}{n^2}\right) \ldots(2)\right]^{1 / n}= $$

$$ \int_{-1}^1 x|x| d x= $$