The 3 videos in this post will take you through a road of calculus building up your conceptual basics thoroughly. The first video will teach you the meaning of a derivative as well as define a viable formula to calculate the derivative of a function at a given point.
Next 2 videos are examples build up the concept into an application form. We will use the first principles rule of differentiation in order to solve the given questions.
What is a derivative?
First Principle rule derivative example 1
First principle rule for derivative example 2