What is the integral of 1 / [e * x + e * (- x)]

What is the integral of 1 / [e * x + e * (- x)]

= e ^ X / (e ^ 2x + 1) integral, = 1 / (e ^ 2x + 1) de ^ x integral, let e ^ x = t, = 1 / (1 + T ^ 2) DT integral = arctant = arctant ^ x (^ refers to power)

If the number of faces and edges of a polyhedron is 6 and 12, then the number of vertices is 8

There is a relationship among the number of vertices V, the number of faces F and the number of edges e of a simple polyhedron. The formula V + F-E = 2 describes the special rules of the number of vertices, the number of faces and the number of edges of a simple polyhedron. Consider a simple polyhedron, subtract one face from it, and then flatten the rest, then V-E + F = 1, and it becomes a net composed of polygons

There is a relation between the number of vertices V, the number of faces F and the number of edges e of a simple polyhedron, V + F-E = 2, which is the famous Euler formula
If f = 2v-4 is true, please explain the reason. If not, please give a counter example

Establishment
V=4　　F=4　　　　E=6
4+4-6=2