Inverse of absolute value function

In summary: You'll have two equations for the inverse. One of them is a line, the other is a parabola.In summary, the conversation discusses finding the equations for the inverse of a function with absolute value. The initial equations are incorrect and the concept of one-to-one functions is discussed. The correct equations are found by restricting the domain and sketching a graph.
  • #1
Coco12
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Homework Statement



Y=abs -4(x+3) +1
Note: the 1 is outside the absolute value

Homework Equations



Switch y and x

The Attempt at a Solution


So you subtract the 1 to bring it to the other side
After that do I put: x-1= -4(y+3)
And x-1= 4(y+3)

And solve for y?

Am I doing this right?? What should be the two equations that you get?
 
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  • #2
Coco12 said:

Homework Statement



Y=abs -4(x+3) +1
Note: the 1 is outside the absolute value
Why not just use the | character? It should be on your keyboard. Also, note that |-4(x + 3)| + 1 = |4(x + 3)| + 1.
Coco12 said:

Homework Equations



Switch y and x

The Attempt at a Solution


So you subtract the 1 to bring it to the other side
After that do I put: x+1= -4(x+3)
And x+1= 4(x+3)

Am I doing this right??
No, you're way off. What happened to the absolute values? When you switch x and y, you should still have both x and y, but in different places. What happened to y here?
Coco12 said:
What should be the two equations that u get?
The only functions that have inverses are those that are one-to-one. Is your function one-to-one?

Textspeak - forum rules do not allow "textspeak," such as "u" for you and so on. Fair warning...
 
  • #3
Opps.. I meant to put x+1=-4(y+3) and so on for the other equation
 
  • #4
I took the positive and negative version for the absolute function.. Is that right?
 
  • #5
You didn't answer my question. Is your function one-to-one?
Coco12 said:
Opps.. I meant to put x+1=-4(y+3) and so on for the other equation
Why is +1 now appearing on the left side?
 
  • #6
The function is not one to one. I'm just trying to determine what the equations for the inverse of the absolute function is. I brought the 1 over from the other side now is just wondering what to do for the stuff inside the absolute value . Do I just take the positive version of it then solve and then the negative version and solve? Is my work above correct?
 
  • #7
Coco12 said:
The function is not one to one. I'm just trying to determine what the equations for the inverse of the absolute function is. I brought the 1 over from the other side now is just wondering what to do for the stuff inside the absolute value . Do I just take the positive version of it then solve and then the negative version and solve? Is my work above correct?
No it's not. "Bringing the 1 over" is not a valid operation. When you started, there was a +1 term on the right side. How do you get rid of it?

Since your function isn't one-to-one, it doesn't have an inverse. However, if you split the domain in the right way, then each part of the function becomes one-to-one, and so has an inverse.

It would be a useful exercise to sketch a graph of y = -4|x + 3| + 1. This might help you figure out how the domain (which is all real numbers) should be split up.
 
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  • #8
I meant to say that it would be x-1=|-4(x+3)|
Where do I go from here assuming that it is one to one?

From my understanding a function does not have to be to one to be an inverse.
One to one simply means that both the function and it's inverse are functions.

I'm trying to find the equation for the inverse
 
  • #9
Coco12 said:
I meant to say that it would be x-1=|-4(x+3)|
If you mean y - 1 = |-4(x + 3)|, then yes.
Coco12 said:
Where do I go from here assuming that it is one to one?
Since it isn't one-to-one, you can't just assume that it is.
Coco12 said:
From my understanding a function does not have to be to one to be an inverse.
No, this is incorrect. For example, y = x2 is not one-to-one, so it does not have an inverse that is a function.
Coco12 said:
One to one simply means that both the function and it's inverse are functions.
That's an outcome of a function being one-to-one, but it isn't the definition. Your book should have a definition of what it means for a function to be one-to-one, and several examples, including at least one where the function is not one-to-one, and what you need to do to find an inverse.
Coco12 said:
I'm trying to find the equation for the inverse
 
  • #10
Let's say we restricted the domain of the original so that we have an inverse. What would be the equations then?
 
  • #11
Have you sketched a graph of y = |-4(x + 3)| + 1? Note that this is exactly the same as y = |4(x + 3)| + 1 = 4|x + 3| + 1.

From the graph it should be fairly obvious how you need to divide the domain.
 

Related to Inverse of absolute value function

1. What is the inverse of an absolute value function?

The inverse of an absolute value function is a function that undoes the effect of the original absolute value function. In other words, it takes the output of the absolute value function and returns the original input value.

2. How do you determine the inverse of an absolute value function?

To determine the inverse of an absolute value function, you switch the roles of x and y and solve for y. This will result in an equation that represents the inverse function.

3. What is the domain and range of the inverse of an absolute value function?

The domain and range of the inverse of an absolute value function are the same as the original absolute value function. The domain is all real numbers and the range is also all real numbers, but it is reflected across the x-axis.

4. Can an inverse of an absolute value function be negative?

No, the inverse of an absolute value function cannot be negative. The absolute value function always returns a positive value, so the inverse function will also return a positive value.

5. How does the graph of an inverse of an absolute value function compare to the original function?

The graph of an inverse of an absolute value function will be a reflection of the original function across the line y = x. This means that any points on the original function will have their x and y coordinates swapped on the inverse function.

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