# Thread: Points for an inverse relation.

1. ## Points for an inverse relation.

I promise, this is the last question for a while.

I need 4 points for the inverse of this relation:

y = 2|x|-1

I dunno how to make absolute values using the MATH button.

But yeah, I did think about substituting 2, 1, -1, -2 in for X, but is that the same as inverse?

2. Originally Posted by mankvill
I promise, this is the last question for a while.

I need 4 points for the inverse of this relation:

y = 2|x|-1

I dunno how to make absolute values using the MATH button.

But yeah, I did think about substituting 2, 1, -1, -2 in for X, but is that the same as inverse?
By inverse relation do you mean inverse function?

If so then consider that

$\forall{x}<0\quad{y=-2x-1}$

and

$\forall{x}>0\quad{y=2x-1}$

3. Originally Posted by Mathstud28
By inverse relation do you mean inverse function?
If so then consider that
you can not consider it inverse function as y=2|x|-1 is not one to one function which is a neccesary condition for a function to have inverse.

4. ## Check this out

I think you really mean inverse relation
y=2|x|-1
y=2x-1 if x>0
x=(y+1)/2>0
x=(y+1)/2 y>-1 or
y=(x+1)/2 x>-1(only interchanged x and y because generally x is taken to represent independent variable)
so we obtained the inverse relation (or inverse function if we particularly talk about y=2x-1 if x>0 as overall y=2|x|-1 do not have an inverse function) similarly same procedure can be followed for y=-2x-1 if x<0. (every function is a relation but every relation is not a function and every function may not have an inverse function)

so here is the easy Method
you said you need 4 points of inverse relation. So put any arbitrary value of x in the equation then interchange the range and domain for example let x=2 then y=2|x|-1
=2|2|-1=3 so the obtained point for relation is (2,3) now interchanging range and domain, point for inverse relation will be (3,2). Remember (3,-2) will also be an element of inverse relation
(3,2) and (3,-2) are not valid points points for a function.

5. Originally Posted by nikhil
you can not consider it inverse function as y=2|x|-1 is not one to one function which is a neccesary condition for a function to have inverse.
They never specified, but based on other problems by this poster, I assumed they accidentally omited a domain on which the function is to be considered, which based on the domain would make the function injective.

EDIT: But thank you very much, I shouldn't assume.