Chapter 5: Problem 42
In Exercises 41–64, find the derivative of the function. $$ f(x)=\ln (x-1) $$
Short Answer
Expert verified
\The derivative of \( f(x) = \ln(x-1) \) is \( f'(x) = \frac{1}{x-1} \).
Step by step solution
01
Identify the function
In this problem, the function \( f(x) \) is given as \( f(x) = \ln(x-1) \). \n\nNotice that the function \( f(x) \) is a logarithmic function. The base of the logarithm is the mathematical constant \( e \), which is approximately equal to 2.71828.
02
Differentiate function
The formula to differentiate the natural logarithm of a function \( u \) is \( \frac{1}{u} * \frac{du}{dx} \). In this case, \( u = x-1 \).\n\nSo, to differentiate \( f(x) = \ln(x-1) \), use the chain rule: first differentiate the outer function, leaving the inner function alone, then differentiate the inner function.\n\nThe derivative of \( \ln(u) \) is \( \frac{1}{u} \), which means the derivative of the outer function is \( \frac{1}{x-1} \).\n\nNext, differentiate the inner function. The derivative of \( x-1 \) is simply 1.
03
Apply the chain rule
Apply the chain rule, multiplying the derivative of the outer function by the derivative of the inner function.\n\nThis gives \( \frac{1}{x-1} * 1 \).
04
Simplify the derivative
The expression \( \frac{1}{x-1} * 1 \) simplifies to \( \frac{1}{x-1} \).\n\nThus, the derivative of \( f(x) = \ln(x-1) \) is \( f’(x) = \frac{1}{x-1} \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Chain Rule
The chain rule is a fundamental tool in calculus used when differentiating composite functions, meaning functions within functions. In the given exercise, the function is \( f(x) = \ln(x-1) \) , a common form where the chain rule applies. Here, you have an outer function, \( \ln(u) \), and an inner function, \( u = x-1 \).
- Start with the outer function: Take its derivative, ignoring the inner details. For \( \ln(u) \), this derivative is \( \frac{1}{u} \) .
- Move to the inner function: Differentiate \( u = x-1 \) which simply gives 1.
Natural Logarithm
The natural logarithm, denoted as \( \ln(x) \), is a logarithm to the base \( e \), the constant approximately equal to 2.71828. It appears frequently in calculus due to its unique properties that simplify differentiation and integration. In the exercise, \( f(x) = \ln(x-1) \), the presence of the natural log signifies a logarithmic function where the concept of working with logs is crucial.
- Recognize that \( \ln(x) \) has a straightforward differentiation formula: its derivative is \( \frac{1}{x} \).
- Understand how natural logs help decompose growth-related problems like compounding (exponential growth).
Differentiation Techniques
Differentiation involves finding the rate at which a function changes at any given point. In calculus, this knowledge is applied using various techniques depending on the type of function. This exercise utilizes a specific differentiation technique tailored for logarithmic functions, particularly key in decomposing functions like \( \ln(x-1) \).
- For \( \ln(x-1) \), utilize the known derivative formula of a logarithm: remain aware that \( f’(x) = \frac{1}{x} \) extends to complex expressions beyond simple variables.
- Apply derivatives carefully — ensuring you adopt accompanying strategies like the chain rule for nested functions.