Chapter 3: Problem 6
Assume that \(f: \mathbb{R} \rightarrow \mathbb{R}\) is invertible and differentiable. Compute \(\left(f^{-1}\right)^{\prime}(4)\) from the given information. $$ f^{-1}(4)=1, f^{\prime}(s)=4+\pi \cos (\pi \mathrm{s}) $$
Short Answer
Expert verified
The value of \((f^{-1})'(4)\) is \(\frac{1}{4 - \pi}\).
Step by step solution
01
Interpret the Given Information
We are provided that \(f^{-1}(4) = 1\), which means that \(f(1) = 4\). The derivative of \(f\) is given as \(f'(s) = 4 + \pi \cos(\pi s)\). We aim to find \(\left(f^{-1}\right)'(4)\).
02
Use the Derivative of the Inverse Function Theorem
The theorem states that if \(f\) is differentiable and its inverse \(f^{-1}\) exists at a point \(f(a)\), then the derivative of the inverse at this point is given by:\[\left(f^{-1}\right)'(f(a)) = \frac{1}{f'(a)} \]Since we have \(f^{-1}(4) = 1\), it follows that \(f(a) = 4\) where \(a = 1\). Therefore, we need \(f'(1)\) to compute \(\left(f^{-1}\right)'(4)\).
03
Compute \(f'(1)\)
Substitute \(s = 1\) into the derivative expression for \(f\):\[f'(s) = 4 + \pi \cos(\pi s)\]\[f'(1) = 4 + \pi \cos(\pi \times 1) = 4 + \pi \cos(\pi)\]Calculate the cosine term: \(\cos(\pi) = -1\), therefore\[f'(1) = 4 + \pi (-1) = 4 - \pi\]
04
Calculate \(\left(f^{-1}\right)'(4)\)
Using the result from Step 2,\[\left(f^{-1}\right)'(4) = \frac{1}{f'(1)} = \frac{1}{4 - \pi}\]
05
Final Answer
The computed derivative of the inverse function at the given point is\[\left(f^{-1}\right)'(4) = \frac{1}{4 - \pi}\].
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Differentiable Functions
Differentiable functions play a pivotal role in calculus. They are functions that have a derivative at each point in their domain. This derivative is a function that provides the slope of the tangent to the curve at each point.
- A function is said to be differentiable if its derivative exists at every point in the domain.
- For a real-valued function of a real variable, say \(f(x)\), the derivative is denoted as \(f'(x)\).
- The existence of the derivative implies continuity, meaning the function doesn't have any abrupt jumps or breaks.
Inverse Function Derivative
The Inverse Function Theorem is a key concept that helps us compute the derivative of an inverse function if it exists. When a function is invertible and differentiable, the theorem offers a way to calculate the derivative of the inverse.
- For a function \(f\) with an inverse \(f^{-1}\), if \(f\) is differentiable at \(a\) and its derivative at \(a\), \(f'(a)\), is not zero, then the inverse function \(f^{-1}\) is differentiable at \(f(a)\).
- The derivative of the inverse function at point \(f(a)\) is given by \(\left(f^{-1}\right)'(f(a)) = \frac{1}{f'(a)}\).
Trigonometric Functions
Trigonometric functions, such as sine and cosine, are fundamental in math, appearing frequently in calculus problems, including derivatives. In our exercise, the derivative of \(f\) involves a trigonometric component: \(4 + \pi \cos(\pi s)\).
- Cosine, denoted as \(\cos(s)\), measures the adjacent side over hypotenuse in a right triangle for an angle \(s\).
- It is a periodic function, meaning its values repeat every \(2\pi\) radians.
- When differentiating functions involving trigonometric parts, recognizing identities and periodic properties of these functions is helpful. For instance, \(\cos(\pi) = -1\).