Name given to certain fundamental relationships between variable quantities and constants.

### Examples

- The formula to calculate the perimeter
*P*of a square of side length*c*is :*P*= 4*c*. - The formula to calculate the volume
*V*of a ball of radius*r*is :*V*= \(\dfrac{4πr^3}{3}\). - Euler’s formula is a formula that relates the number of vertices
*S*, the number of faces*F*and the number of edges*A*of a convex polyhedron :*S*+*F*=*A*+ 2.