Courses on Khan Academy are always 100% free. Start practicing—and saving your progress—now: https://www.khanacademy.org/math/multivariable-calculus/applications-of-multivariable-derivatives/lagrange-multipliers-and-constrained-optimization/v/the-lagrangian How a special function, called the "Lagrangian", can be used to package together all the steps needed to solve a constrained optimization problem.