Hi..I have a basic question regarding the equation of an ellipse. Lets say I ahve an ellipse with major and minor axes 2a and 2b respectively. Now, to check whether a point lies inside this ellipse, its fairly simple...I can just use the standars ellipse equation for that. Now, if my major axis is rotates to..lets say 45 degrees, how does the equation of the ellipse vary and how do I find then whether a certain point lies within the ellipse?? Logically, rotation of the major axis must not change the way I look for a point to be located inside/outside an ellipse. except that lets say once the rotation angle is >= 90 degrees your major axis becomes minor an vice-versa. Is my thinking correct?? or does the equation and method vary??? I'd really appreciate it if someone can throw me some pointers...thanks.. PS: Before any1 asks, this is not a homework problem..am a workign professional..cheers!!!