Natural Logarithm Function and Properties
The page introduces the fundamental concepts and properties of the natural logarithm function, known in French as fonction logarithme népérien.
Definition: The natural logarithm of a strictly positive real number a is defined as the unique solution to the equation eˣ = a, denoted as lna.
Vocabulary: The domain of the natural logarithm function is 0,+∞, mapping to all real numbers.
Highlight: The exponential and natural logarithm functions are inverse functions of each other, with their graphs being symmetric about the line y = x.
Key Properties:
- The function is differentiable on 0,+∞ with derivative 1/x
- It is strictly increasing and concave on its domain
- Essential limits include limx→0+ lnx = -∞ and limx→+∞ lnx = +∞
Example: Important identities include:
- lnxy = lnx + lny
- lnx/y = lnx - lny
- ln√x = ½lnx
- lnxn = nlnx
Highlight: The function's behavior at key points includes:
- ln1 = 0
- lne = 1
- For any x, y > 0: lnx < lny if and only if x < y
The page concludes with important limit properties and composition rules, essential for advanced calculus applications.