Properties of the derivative
We now consider various properties of differentiation. As we proceed, we will be able to differentiate wider and wider classes of functions.
Throughout this section and the next, we will be manipulating limits as we compute derivatives. We therefore recall some basic rules for limits; see the module Limits and continuity for details. The following hold provided the limits and exist.
- The limit of a sum (or difference) is the sum (or difference) of the limits:
- The limit of a product is the product of the limits:This includes the case of multiplication by a constant :
The derivative of a constant multiple
Suppose we want to differentiate . Rather than returning to the definition of a derivative, we can use the following theorem.
Theorem
Let be a differentiable function and let be a constant. Then the derivative of is . That is,
This fact can also be written in Leibniz notation as
Proof
The derivative of is given by
We may factor out the , since it is just a constant.
Example
What is the derivative of ?
Solution
The theorem tells us that the derivative of is 4 times the derivative of . Hence,
0 Comments