The expression 1 - r^n is commonly found in mathematics, particularly in the context of geometric series. Here, r represents the common ratio, and n indicates the number of terms in the series. This formula helps calculate the sum of a geometric series when the first term is 1, providing a way to understand how the series converges or diverges based on the value of r. In practical applications, 1 - r^n can be used in finance to determine the present value of annuities or in physics to analyze decay processes. Understanding this expression is essential for solving problems related to exponential growth or decay, making it a valuable tool in various fields such as economics and engineering.