Goldstein's Theorem is a concept in the field of mathematics, specifically in the study of differential equations. It provides conditions under which certain types of solutions exist for a class of nonlinear differential equations. This theorem is particularly useful in understanding the behavior of solutions in various mathematical models. The theorem is named after S. Goldstein, who contributed to the development of mathematical theories in the mid-20th century. Goldstein's work has implications in physics and engineering, where differential equations are commonly used to model dynamic systems and phenomena.