Help finding a inverse function

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Homework Help Overview

The discussion revolves around finding inverse functions for given equations, specifically for the functions f(x)=2x^3+5x+3 and f(x)=x^3/(x^2+1). The original poster seeks to determine the values of x when f^-1(x) is set to specific values.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to express the inverse functions explicitly but encounters difficulties. Some participants suggest that explicit forms may not be necessary for solving the problem, while others express curiosity about the complexity of finding such forms for higher-degree polynomials.

Discussion Status

The discussion has progressed with some participants providing guidance on the approach to take, indicating that evaluating f(1) could be a simpler alternative to finding the explicit inverse. There is an acknowledgment of the challenges associated with higher-degree equations, with references to Galois theory and the limitations of finding explicit solutions.

Contextual Notes

Participants note the complexity of deriving explicit forms for cubic and quartic functions, and the lack of general formulas for fifth-degree polynomials or higher, which may influence the approach to the problem.

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Homework Statement


Given that f(x)=2x^3+5x+3 and f^-1(x)=1 then find the value of x
Given that f(x)=x^3/(x^2+1) and f^-1(x)=2 then find the value of x

Homework Equations



I got to the eqn x=2Y^3+5Y+3 & X=Y^3/(Y^2+1)


The Attempt at a Solution



But now i m in trouble finding the f^-1(x) in explicit form to use the value of f^-1(x)
 
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You are going to have a hard time finding explicit forms. But you don't have to. If e.g. f^(-1)(x)=1, then x=f(1), yes?
 
Thanks that got my problem solved :D
But i m just curious to know how to find that big cubic or quadratic functions in explicit mode :)
 
If it cubic or quartic, there are formulas, but they are too complicated for most practical uses. If it's fifth degree or worse there are no formulas, except in special cases. There are proofs of this, it's called Galois theory.
 

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