When I rotate an object how do I rotate back? - actionscript-3

Question

I'm on a code/maths task where I need to rotate a shape to 0 degrees and then back to whatever degrees it was at in the first place.
The following method:
function rotateAroundOrigin(xPos:Number, yPos:Number, angle:Number, origin:Point):Point {
var point:Point = new Point();
angle *= Math.PI / 180;
point.x = Math.cos(angle) * (xPos - origin.x) + Math.sin(angle) * (yPos - origin.y) + origin.x;
point.y = Math.sin(angle) * (xPos - origin.x) - Math.cos(angle) * (yPos - origin.y) + origin.y;
return point;
}
Is invoked twice like so:
var rotatePoint:Point = rotateAroundOrigin(30, 30, -90, midPoint);
var rotatePointBack:Point = rotateAroundOrigin(30, 30, -90, midPoint);
It works fine but it doesn't make sense that it works because the degrees value is "-90" both times it's rotated. It should be "-90" to rotate one way and then "90" to rotate back to where it was in the first place.
Anyone have any ideas how I can modify the "rotateAroundOrigin" method so you can invoke with "-90" then with "90" like so?
var rotatePoint:Point = rotateAroundOrigin(30, 30, -90, midPoint);
var rotatePointBack:Point = rotateAroundOrigin(30, 30, 90, midPoint);

Answer 1

var rotatePoint:Point = rotateAroundOrigin(30, 30, -90, midPoint);
var rotatePointBack:Point = rotateAroundOrigin(30, 30, -90, midPoint);
It looks like you're just doing the same thing twice: rotating the point (30, 30) around midPoint. Consider this:
var rotatePoint:Point = rotateAroundOrigin(30, 30, -90, midPoint);
var rotatePointBack:Point = rotateAroundOrigin(rotatePoint.x, rotatePoint.y, 90, midPoint);
EDIT: I also noticed that you mixed up some signs in the rotation method. Try this:
function rotateAroundOrigin(xPos:Number, yPos:Number, angle:Number, origin:Point):Point {
var point:Point = new Point();
angle *= Math.PI / 180;
point.x = Math.cos(angle) * (xPos - origin.x) - Math.sin(angle) * (yPos - origin.y) + origin.x;
point.y = Math.sin(angle) * (xPos - origin.x) + Math.cos(angle) * (yPos - origin.y) + origin.y;
return point;
}