System.Drawing.Graphics.computeFocii C# (CSharp) Method

        private void computeFocii()
        {
            double d = Math.Sqrt(a * a - b * b);
            double dx = d * cosTheta;
            double dy = d * sinTheta;

            xF1 = cx - dx;
            yF1 = cy - dy;
            xF2 = cx + dx;
            yF2 = cy + dy;
        }