Chapter 7: Problem 41
Use (8) to calculate \(\left(f^{-1}\right)^{\prime}(c) .\) (Hint: Find \(a\) by inspection.) $$ f(x)=x^{3}+7 ; c=6 $$
Short Answer
Expert verified
\((f^{-1})'(6) = \frac{1}{3}\).
Step by step solution
01
Understand the Problem
We are given a function \( f(x) = x^3 + 7 \) and the value \( c = 6 \). We need to find \( (f^{-1})'(c) \), which is the derivative of the inverse function evaluated at \( c \).
02
Find \( a \) such that \( f(a) = c \)
To find \( a \), we need to solve the equation \( f(a) = 6 \). Substitute into the function: \( a^3 + 7 = 6 \). Simplifying gives: \( a^3 = -1 \) so \( a = -1 \).
03
Apply the Inverse Function Derivative Formula
The formula for the derivative of the inverse function is \( (f^{-1})'(c) = \frac{1}{f'(a)} \). We previously found \( a = -1 \). We now need to compute \( f'(x) \) and substitute \( a \) into it.
04
Differentiate \( f(x) \)
Find the derivative of \( f(x) = x^3 + 7 \). The derivative, \( f'(x) = 3x^2 \).
05
Evaluate \( f'(a) \)
Substitute \( a = -1 \) into the derivative: \( f'(-1) = 3(-1)^2 = 3 \).
06
Calculate \( (f^{-1})'(c) \)
Using the formula \((f^{-1})'(c) = \frac{1}{f'(a)}\), substitute in the value we found: \((f^{-1})'(6) = \frac{1}{3}\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Inverse Functions
Inverse functions help us find the input needed to obtain a specific output from a function. They are essentially the reverse of the original function. Here, finding the inverse of a function allows us to trace back from the output \( c \) to the original input \( a \).
Consider a function \( f(x) \) and its inverse \( f^{-1}(x) \). If \( f(x) = y \), then \( f^{-1}(y) = x \). Thus, \( f(f^{-1}(y)) = y \) and \( f^{-1}(f(x)) = x \). This reciprocal relationship is crucial because it allows us to revert any function back to its starting value using \( f^{-1} \).
You need to find the inverse at a specific point when dealing with calculus problems, just like we found \( f^{-1}(c) \) to solve \( f(a) = c \). In the context of derivates, the inverse function allows us to handle outputs that need to be traced back to their inputs.
Consider a function \( f(x) \) and its inverse \( f^{-1}(x) \). If \( f(x) = y \), then \( f^{-1}(y) = x \). Thus, \( f(f^{-1}(y)) = y \) and \( f^{-1}(f(x)) = x \). This reciprocal relationship is crucial because it allows us to revert any function back to its starting value using \( f^{-1} \).
You need to find the inverse at a specific point when dealing with calculus problems, just like we found \( f^{-1}(c) \) to solve \( f(a) = c \). In the context of derivates, the inverse function allows us to handle outputs that need to be traced back to their inputs.
Derivatives
Derivatives provide information about the rate at which a function is changing at any given point. They are the foundation of calculus and crucial in function analysis.
The derivative of \( f(x) = x^3 + 7 \) can be found using basic differentiation rules. When differentiating, constants like 7 disappear, leaving us with the derivative of \( x^3 \), which is \( 3x^2 \).
This derivative formula, \( f'(x) = 3x^2 \), allows us to compute the gradient, or slope, of the tangent to the curve at any point \( x \). In the context of inverse functions, once \( f'(x) \) is known, it helps in finding \( (f^{-1})'(x) \) using the inverse function derivative formula.
The derivative of \( f(x) = x^3 + 7 \) can be found using basic differentiation rules. When differentiating, constants like 7 disappear, leaving us with the derivative of \( x^3 \), which is \( 3x^2 \).
This derivative formula, \( f'(x) = 3x^2 \), allows us to compute the gradient, or slope, of the tangent to the curve at any point \( x \). In the context of inverse functions, once \( f'(x) \) is known, it helps in finding \( (f^{-1})'(x) \) using the inverse function derivative formula.
Function Analysis
Function analysis involves examining the properties and behaviors of a function. By analyzing a function, you can gain insights into its growth, shrinkage, slopes, and more specifically, invertibility in some cases.
In our exercise with \( f(x) = x^3 + 7 \), analyzing the function first involves understanding why it can be inverted. Since it's a cubic function, it's non-linear but monotonic (always increasing or decreasing), thus having an inverse over all real numbers.
To solve the equation \( f(a) = 6 \), we set \( x^3 + 7 = 6 \) and solve for \( x \), indicating the output where the function achieves this value. This process helps us find the required value of \( a \), allowing further analysis in subsequent steps of the problem.
In our exercise with \( f(x) = x^3 + 7 \), analyzing the function first involves understanding why it can be inverted. Since it's a cubic function, it's non-linear but monotonic (always increasing or decreasing), thus having an inverse over all real numbers.
To solve the equation \( f(a) = 6 \), we set \( x^3 + 7 = 6 \) and solve for \( x \), indicating the output where the function achieves this value. This process helps us find the required value of \( a \), allowing further analysis in subsequent steps of the problem.
Mathematical Problem-Solving
Mathematical problem-solving is an approach that combines logical reasoning, concept understanding, and strategy application to find solutions.
When solving for \((f^{-1})'(c)\), we follow a structured method:
When solving for \((f^{-1})'(c)\), we follow a structured method:
- Understanding the problem and identifying known elements.
- Finding \( a \) such that \( f(a) = c \) by solving the equation \( a^3 + 7 = c \).
- Using established mathematical techniques, such as differentiation, to find \( f'(x) \).
- Working through formulas like \( (f^{-1})'(c) = \frac{1}{f'(a)} \) to find the desired inverse derivative.