EaseOutBack Easing Animations (Maths!)

Hi all,

Maths was never my strong suit, but I've managed to make this following code work for bringing in a menu from the right hand side of a screen with a button press, and then moving it back off screen, using a Cosine function to smoothly adjust the X property:

Switch(true,
 flyOut,
//Begins on-screen and moves off-screen, using Cosine to smoothly subtract a fraction of the Rectangle's full width at a time
//Starting Position on-screen

 ((Parent.Width - Self.Width) - 10) +

//Gradually add the width of the rectangle

 (-Self.Width - 10) * Cos(MenuTimer.Value/MenuTimer.Duration * (Pi()/2)) + (Self.Width + 10),


 !flyOut,
//This takes the box from off-screen to on-screen, beginning with it's position being equal to the width of the screen
//Starting position off-screen

 Parent.Width -

//Gradually add the width of the rectangle

 ((-Self.Width - 10) * Cos(MenuTimer.Value/MenuTimer.Duration * (Pi()/2)) + (Self.Width + 10))
)

I adapted this from the fantastic work of @Mr-Dang-MSFT to make it work on the right-hand side of the screen.

What I would like now is to see if I can make it do this with the EaseOutBack version, giving it a little bounce on the way out. Does anyone know at all how to make this happen? I guess it's nowhere near as simple of the Cosine version as we're technically adding a few extra pixels of movement just before it reaches it's final position just on screen.

-Edit-

I have included a gif of what it currently does: