Is the Function f(x) = x^5 - x^3 + 2x Invertible?

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Homework Help Overview

The discussion revolves around the function f(x) = x^5 - x^3 + 2x and its invertibility. Participants are tasked with demonstrating the function's invertibility and computing the derivative of its inverse at a specific point.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss the process of finding the inverse by switching variables and express uncertainty about solving for y. There are questions regarding the properties of the function, particularly its increasing nature, as a means to establish invertibility.

Discussion Status

The discussion is ongoing, with participants exploring the conditions necessary for a function to be invertible. Some guidance has been offered regarding the need to demonstrate that the function is increasing, but there is no explicit consensus on the approach to take.

Contextual Notes

Participants are navigating the requirements of the homework prompt, which asks for proof of invertibility rather than the actual computation of the inverse. There is a focus on understanding the implications of the function's derivative.

alexs2jennisha
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Homework Statement



1. Show that the function f(x) = x5 -x3 +2x is invertible. Compute the derivative of f-1
at 2.


The Attempt at a Solution


To find f-1 I switched x and y which gave me x = y5 - y3 + 2y

this is where i got stuck because I am not sure how to solve for y after that step.

Can the y5 - y3 become y2?

Thanks
 
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alexs2jennisha said:

Homework Statement



1. Show that the function f(x) = x5 -x3 +2x is invertible. Compute the derivative of f-1
at 2.


The Attempt at a Solution


To find f-1 I switched x and y which gave me x = y5 - y3 + 2y

this is where i got stuck because I am not sure how to solve for y after that step.
Lucky for you, you weren't asked to calculate ##f^{-1}##, just show it exists. Can you show, for example, that ##f## is increasing?
Can the y5 - y3 become y2?

Of course not.
 
alexs2jennisha said:
Can the y5 - y3 become y2?

one really good way to see if numeric algebra works is to take a simple case and see what happens. what if [itex]y=1[/itex]?? then you know the answer to be zero yet if you adopt your proposition we see the answer is 1, which is of course incorrect.

hope this helps for the future
 
What is necessary for a function to be invertible ?
 

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