Purpose of the derivative of the inverse function

In summary, the conversation discusses the derivative of the inverse function in calculus, which is represented as g'(x) = 1/f'(g(x)). The conversation also includes a question about its practical applications, with an example of controlling engine speed with a dial. The derivative of arccos(x) is also mentioned, with its relation to the inverse function. Overall, the conversation highlights the usefulness of this property in various fields, such as physics and trigonometry.
  • #1
barryj
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Homework Statement


In calculus, I learn that the derivative of the inverse function is

g'(x) = 1/ f'(g(x))

Homework Equations


So..

The Attempt at a Solution



Can someone give me an example of where I need to know this, or is this just a math exercise. Is there a relatively simple physics example?
 
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  • #2
Sure. Suppose you are controlling an engine speed with a dial. If you want to increase the speed by 3 rpm, how much should you increase the dial setting?

PS. Keep in mind that this gives a linear estimate at that setting. It maybe very different at another setting.
 
  • #3
Don't go away for long. I will be back in4 hours.
 
  • #4
This property of the derivative of the inverse function is just a simple observation of what a slope is when looked at from another direction. As such, it has applications everywhere.
 
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  • #5
What is the derivative of ##\arccos x##? Good luck with using the definition.
 
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  • #6
OK, finding the derivative of arccos(x)
given... f(x) = cos(X) and g(x) = cos^-1(x)

then g'(x) = 1/f'(g(x))

g'(x) = 1/-sin(g(x))

g'(x) = 1/-sin(cos^-1(x))

then after some trig substitutions we get this is equal to ##-1/\sqrt(1-u^2)##or something like this.
 
  • #7
barryj said:
OK, finding the derivative of arccos(x)
given... f(x) = cos(X) and g(x) = cos^-1(x)

then g'(x) = 1/f'(g(x))

g'(x) = 1/-sin(g(x))

g'(x) = 1/-sin(cos^-1(x))

then after some trig substitutions we get this is equal to ##-1/\sqrt(1-u^2)##or something like this.

This is one of the numerous examples where it is useful.
 
  • #8
Could someone give me a few more examples where finding the derivative of the inverse function is useful.
 

1. What is the purpose of the derivative of the inverse function?

The purpose of the derivative of the inverse function is to determine the rate of change of the original function at a specific point. It allows us to find the slope of the tangent line to the inverse function at a given point.

2. How is the derivative of the inverse function related to the original function?

The derivative of the inverse function is the reciprocal of the derivative of the original function. This means that if the derivative of the original function is 1/x, then the derivative of the inverse function is x. This relationship is known as the inverse function theorem.

3. Why is the derivative of the inverse function important?

The derivative of the inverse function is important because it allows us to find the slope of the tangent line to the inverse function, which can be used to solve optimization problems and find critical points. It also helps us understand the behavior of the original function and its inverse.

4. Can the derivative of the inverse function be negative?

Yes, the derivative of the inverse function can be negative. This means that the original function is decreasing at that point. However, the absolute value of the derivative of the inverse function will be equal to the absolute value of the derivative of the original function.

5. Is there a specific formula for finding the derivative of the inverse function?

Yes, the formula for finding the derivative of the inverse function is (f^-1)'(x) = 1/f'(f^-1(x)), where f'(x) is the derivative of the original function and f^-1(x) is the inverse function. This formula can be derived using the chain rule and the inverse function theorem.

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