Expert advice need please :)

Hi guys, hope you can help me with this, it's been bugging me for two days now, and feel like I've gone no where with it

I wanted to have an 'inverted control' in my game, sort of like how they have in FPS games, but pivot around a central object.

For example:

I want to move my mouse up and my cross-hair image/object should move down, move mouse left and cross-hair moves right, etc. As the mouse gets closer to the center, the cross-hair moves inwards, and moves outwards when you move the mouse away from the center.

I'm not good with maths and tried for two days using the built-in expressions etc to get values, but having no luck. I know it can be done by the more experienced users, but I don't have any clues what I could try now.

I will upload an MFA of the file when I jump on my laptop again, but if anyone is struggling to understand what I'm trying to achieve, please tell me.

Also, an example MFA isn't a must, just some simple instructions will help too. Thanks in advance guys!

I'll upload the file in a bit so you guys can see what I'm trying to do.

Eg: In some first person shooters, if you move your joystick down, the camera looks up, and vice versa.
Here's a MFA file similar to what I wanted to do, but I don't want the cross hair to be where the mouse pointer is or the arrow to point at the mouse position. I do want the arrow to be the centre of everything, so the cross-hair rotates around the centre...

I don't know how to use the expressions editor properly, or Cos and Sin formulas, so I don't have a clue how to do this...

Sorry I guess I wasn't being clear! What I wanted to do was create something that replicates a 'slingshot' mechanic. You hold and drag the middle of the slingshot and a cross hair shows where your bullet will land when the user lets go of the sling. I will definitely check out the file when I get home, thanks Skyhunter.