This lecture covers linear first-order differential equations, defining them as implicit relations between a function and its derivatives. It explains the trajectory and motion concepts related to these equations, along with the terminology of linear differential equations. The lecture delves into homogeneous and inhomogeneous cases, providing examples and solutions. It also discusses the uniqueness of solutions with initial conditions and presents the theorem for finding particular solutions. The lecture concludes with practical applications and methods for solving linear first-order differential equations.