$$\int \frac{1+2 e^{-x}}{1-2 e^{-x}} d x=$$

If the volume of the parallelopiped whose conterminus edges are along the vectors $$\mathbf{a}, \mathbf{b}, \mathbf{c}$$ is 12, then the volume of the tetrahedron whose conterminus edges are $$\mathbf{a}+\mathbf{b}, \mathbf{b}+\mathbf{c}$$ and $$c+a$$ is

The function $$f(x)=\frac{x+1}{9 x+x^3}$$ is

For any non-zero vectors $$\mathbf{a}$$ and $$\mathbf{b}$$,