Stirling's approximation for factorials, expressed as x! ~ sqrt(2πx)(x/e)^x, is derived through mathematical analysis involving limits and integrals. The approximation provides a way to estimate large factorials efficiently. A detailed step-by-step derivation can be found in the article shared from Mathworld. This resource clarifies the underlying principles and calculations involved in the approximation. Understanding Stirling's approximation is essential for applications in statistics and combinatorics.