Formula of offset x point

Hi,

I have two sets of X,Z coordinates which represent the start and end of a line. The line between the two points is at a random angle.

I want to work out the X,Y coordinates of a line which is, say, 500 units offset to one side.

I've found I can use  Autodesk.Revit.DB.Curve.CreateOffset to work out the coordinates I require, but this draws a line - which I don't want, I simply want to work out the coordinate values.

Is there any API member I can use to do this, or is there a simple formula that I can use to calc the coordinates?

Thanks.