Famous mathematical problems featuring pi

Area = (pi)radius2

Circumference = (pi)diameter

The cosmological constant

Heisenberg's uncertainty principle

Einstein's field equation of general relativity

Coulomb's law for the electric force, describing the force between two electric charges (q1 and q2) separated by distance r

Magnetic permeability of free space

Kepler's third law constant, relating the orbital period (P) and the semimajor axis (a) to the masses (M and m) of two co-orbiting bodies