Inverse of f(x): Is it a Function or Relation?

In summary, the conversation discusses finding the inverse of a given function and determining whether it is a function or a relation. The solution involves making x the subject and checking its validity by substituting test values.
  • #1
Monocerotis
Gold Member
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0

Homework Statement



Find the inverse of each function. Is the inverse a function or a relation ?

f(x) = (x-4)/3



The Attempt at a Solution


Not sure which one is correct, and if any are not sure why (as in rules that may apply)

f(x) = (x-4)/3
f^-1(x) = 3x+4

or

f^-1 3x+12
 
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  • #2
A way I usually approach such questions is by letting y = f(x), then making x the subject. Clearly then, the expression (in y) will give the inverse function.

Another way would be by observing that
[tex]f^{-1} (\frac{x - 4}{3}) = x = (\frac{x - 4}{3}) (3) + 4[/tex]

You can always check the validity of your function by substituting test values.
 
  • #3
= x

The inverse of a function is a relation that switches the inputs and outputs of the original function. In this case, the inverse of f(x) is f^-1(x) = 3x + 4. This is a function because for every input x, there is only one output, satisfying the definition of a function. The second attempt at finding the inverse, f^-1(3x+12) = x, is incorrect because it does not satisfy the definition of a function. For example, if x=0, then f^-1(3x+12) = 12, but if x=1, then f^-1(3x+12) = 15, which means there are two different outputs for the same input, violating the definition of a function. Therefore, the inverse of f(x) is a function, not a relation.
 

Related to Inverse of f(x): Is it a Function or Relation?

1. What is the definition of an inverse function?

The inverse function of f(x) is a function that, when applied to the output of f(x), returns the input of f(x). In other words, if we have a function f(x) and its inverse function g(x), then g(f(x)) = x and f(g(x)) = x.

2. How do you determine if the inverse of a function is a relation or a function?

To determine if the inverse of a function is a relation or a function, we must check for one-to-one correspondence. This means that each input of the original function must correspond to only one output, and each output must correspond to only one input. If this is the case, then the inverse is a function. If not, then the inverse is a relation.

3. Can a function have more than one inverse?

No, a function can only have one inverse. This is because an inverse function must pass the vertical line test, meaning it must have a one-to-one correspondence between its inputs and outputs. If there were more than one inverse, then the function would fail the vertical line test.

4. How do you find the inverse of a function?

To find the inverse of a function, we can use a process called "switching x and y." This means that we swap the x and y variables in the original function and solve for y. The resulting function will be the inverse of the original function.

5. Can all functions have an inverse?

No, not all functions have an inverse. For a function to have an inverse, it must be a one-to-one function, meaning each input has a unique output. If a function is not one-to-one, then it does not have an inverse. For example, the function f(x) = x^2 does not have an inverse because multiple inputs can result in the same output.

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