Finding the Inverse of Cubic Functions

In summary, the inverse of a cubic function is a function that undoes the original cubic function, and it can be found by switching the x and y variables and solving for y. The domain and range of the inverse function are switched compared to the original function, and a cubic function can only have one inverse. To determine if a cubic function has an inverse, you can use the horizontal line test or the vertical line test.
  • #1
devious_
312
3
Is there a way (algebraic or otherwise) to find the inverse function of a cubic polynomial?

For example:
y(x) = x³+x-9
y-1(x) = ?
 
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  • #2
Yes but it is big and nasty.

In the same way you can have:

[tex]y = ax^2 + bx + c[/tex]

[tex]ax^2 + bx + (c - y) = 0[/tex]

[tex]x = \frac{-b \pm \sqrt{b^2 - 4a(c-y)}}{2a}[/tex]

You can do it for cubic equations with this equation: http://www.math.vanderbilt.edu/~schectex/courses/cubic/
 
  • #3
Thanks. Just what I was looking for.
 

1. What is the definition of an inverse of a cubic function?

The inverse of a cubic function is a function that undoes the original cubic function. In other words, if the original cubic function takes an input and produces an output, the inverse function takes that output and produces the original input.

2. How do you find the inverse of a cubic function?

To find the inverse of a cubic function, you can follow these steps:1. Write the original function in the form f(x) = ax^3 + bx^2 + cx + d.2. Replace f(x) with y.3. Switch the x and y variables so that the equation becomes x = ay^3 + by^2 + cy + d.4. Solve for y using algebraic methods.5. Replace y with f^-1(x) to represent the inverse function.

3. What is the domain and range of the inverse of a cubic function?

The domain of the inverse of a cubic function is the range of the original cubic function, and the range of the inverse function is the domain of the original cubic function. In other words, the inputs and outputs of the inverse function are switched compared to the original function.

4. Can a cubic function have more than one inverse?

No, a cubic function can only have one inverse. This is because for a function to have an inverse, it must pass the horizontal line test, which means every horizontal line intersects the function at most once. Since cubic functions are one-to-one, they will have only one inverse.

5. How can you tell if a cubic function has an inverse?

A cubic function has an inverse if it passes the horizontal line test. This means that every horizontal line intersects the function at most once. Visually, this can be seen as a graph that does not have any horizontal lines passing through more than one point. Algebraically, you can use the vertical line test to check if a function has an inverse.

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