Retrieve a positive or a negative angle from 3 points

Question

I am rotating points around a center point in 2D space. The points are the center point, the old mouse position, and the new mouse position. My rotation function works fin

Answer 1

Try this, but I'm not sure:

double v1x = Xb - Xc;
double v1y = Yb - Yc;
double v2x = Xa - Xc;
double v2y = Ya - Yc;

double angle = Math.Atan2(v1x, v1y) - Math.Atan2(v2x, v2y);