This lecture focuses on correcting exercise 1 of series 4, which deals with first-order differential equations. The exercise involves an object of mass m in vertical free fall under the influence of gravity and air friction forces. The lecture covers the vertical nature of the problem, the forces acting on the object, and the derivation of the differential equation of motion. The instructor explains the projection of forces, the transformation of vectorial equations into scalar ones, and the resolution of the differential equation. The process includes making the equation homogeneous, finding the solution, determining horizontal and oblique asymptotes, and graphically representing the results.