Lagrange Interpolation:

This technique is rather useful for programming in digital computer. In this, a revised form of quadratic equation (known as the 2nd order Lagrange polynomial) is utilized. Here (x₁, y₁), (x₂, y₂) & (x₃, y₃) are the data points available to determine the three constants

That means      y = f (x) = c₁ (x - x₂) (x - x₃) + c₂ (x - x₁) (x - x₃) + c₃ (x - x₁) (x - x₂) By setting x = x₁, x₂ and x₃, we get

The common form of the n - 1 degree Lagrangian polynomial is

Here the sign Π refers multiplication.