The expression "n_1^2" represents the square of a variable, typically denoted as n_1. In mathematics, squaring a number means multiplying it by itself. For example, if n_1 equals 3, then n_1^2 would equal 9, since 3 multiplied by 3 is 9. This notation is commonly used in various fields, including algebra and physics, to simplify equations and represent relationships. Squaring a variable can help in solving problems involving areas, such as the area of a square, where the area is calculated as the side length squared, or n_1^2.