The Natural Exponential Function
is continuous and increasing one-to-one.
It has an inverse function.
We will call it the natural exponential function, denoted as .
Domain of is the range of : .
Range of is the domain of : .
for any .
for ant .
What is the derivative of ?
Derivative of Inverse Functions
Derivative of an Inverse Function
Theorem: If a function is a one-to-one function with inverse , and is a number such that:
- is differentiable at and
- ,
then is differentiable at and
The Exponential Function
Let . Find .
Derivative of Exponential Function
The exponential function is differentiable everywhere and
Since , the natural exponential function is increasing.
Since is increasing, the natural exponential function is concave up.
The Natural Base
Define , so that .
Suppose is a rational number. Then for any , .
Applying the exponential function on both sides: .
Since and are inverse to each other, they cancel: .
This gives us .
If , then , which gives us .
For a rational number , .
Irrational Powers
If is an irrational number, we define to be .
Then for any real number .
General powers:
Suppose and are real numbers, and . Define .
Other Properties of
Let and be two real numbers. Let .
Summary
Domain of is the range of : .
Range of is the domain of : .
for any .
for ant .
is increasing and concave up.