This lecture covers the concepts of derivatives and approximations, focusing on logarithmic functions. It explains the definition of the derivative, higher-order derivatives, and the theorem of local extrema. The lecture also delves into the lateral derivatives of logarithmic functions, showcasing examples and calculations. Emphasis is placed on understanding the derivative of reciprocal functions and the continuity of differentiable functions. Various techniques for deriving and approximating logarithmic functions are explored, providing a comprehensive overview of the topic.