Topic: Elementary Calculus
Subtopic: Differentiation
Rationale:
In mathematics, differential calculus is a subfield of calculus that studies the rates at which quantities change.[1] It is one of the two traditional divisions of calculus, the other being integral calculus—the study of the area beneath a curve.[2]
The primary objects of study in differential calculus are the derivative of a function, related notions such as the differential, and their applications. The derivative of a function at a chosen input value describes the rate of change of the function near that input value. The process of finding a derivative is called differentiation. Geometrically, the derivative at a point is the slope of the tangent line to the graph of the function at that point, provided that the derivative exists and is defined at that point. For a real-valued function of a single real variable, the derivative of a function at a point generally determines the best linear approximation to the function at that point. https://en.wikipedia.org/wiki/Differential_calculus