This document discusses interpolation methods for unequal intervals, specifically Lagrange's interpolation formula. It provides an example of using Lagrange's formula to compute an interpolated value f(9.2) given data points with unequal x-values of 9, 9.5, and 11 and their corresponding f-values. The interpolation is calculated and the result is 2.2191. Lagrange's formula is applicable to problems with equal or unequal intervals between data points and is preferable for unequal intervals. It involves multiplying and dividing polynomials based on the given x-values and f-values.