In mathematics, Lagrange's theorem usually refers to any of the following theorems, attributed to Joseph Louis Lagrange:
Lagrange's theorem (group theory) Lagrange's theorem (number theory) Lagrange's four-square theorem, which states that every positive integer can be expressed as the sum of four squares of integers Mean value theorem in calculus The Lagrange inversion theorem The Lagrange reversion theorem The method of Lagrangian multipliers for mathematical optimization