How to drive a value with linear fcurve on both positive and negative axis? Like for example:

I have a constraint on object A,
B is driving the constraint influence.

If I move B in +X axis 0 to 1, the influence on A is going 1 to 0 on a linear fcurve.
I want to add the same thing on object B's -X axis with linear fcurve
I am not very well versed with scripting but I am trying to get some math right to give it gradual decrease using scripted expressions, but would there be any other way to achieve that?
Thanks
(attached image just for an understanding)

Added blender sample file
Sample Eye Brows created in the file:
Main Controller -&gt; (AnimConstraint) BrowsIn, (Copy Location) MCH.Driver
MCH.Driver -&gt; (AnimConstraint) BrowsAngry,BrowsSad
So when you take the main controller straight on z axis to the right, it triggers brows in. Take the main controller up/down while being on the right, it affects MCH.Driver to go up/down.
So when my MCH.Driver is on Y : 0 and Main Controller goes right, Brows in gets triggered
Now I take MainController to bottom , angry gets triggered and BrowsIn reduces
(because i have set driver on the influence of BrowsIn. When MCH.Driver goes down, it reduces the influence; same way if it can be applied when it goes up, problem would be solved)
Now I take Maincontroller up (topright) its goes BrowsIn + BrowsSad where I only want to trigger BrowsSad and reduce BrowsIn again like the BrowsAngry trigger..
I hope it wasn't confusing ^^
Solved it with abs() function!

abs(var) 

and it affected in the same way in both positive and negative values! :)