Lagrange's theorem

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