Euler’s formula
- Related Topics:
- mathematics
- Euler’s theorem on polyhedrons
- On the Web:
- Rose-Hulman Scholar - An Appreciation of Euler's Formula (PDF) (May 17, 2025)
Euler’s formula, either of two important mathematical theorems of Leonhard Euler. The first formula, used in trigonometry and also called the Euler identity, says eix = cos x + isin x, where e is the base of the natural logarithm and i is the square root of −1 (see imaginary number). When x is equal to π or 2π, the formula yields two elegant expressions relating π, e, and i: eiπ = −1 and e2iπ = 1, respectively. The second, also called the Euler polyhedra formula, is a topological invariance (see topology) relating the number of faces, vertices, and edges of any polyhedron. It is written F + V = E + 2, where F is the number of faces, V the number of vertices, and E the number of edges. A cube, for example, has 6 faces, 8 vertices, and 12 edges and satisfies this formula.