public static double FindAngle(LineSegment fLine, LineSegment sLine) { var v1 = fLine.ConvertToVector(); var v2 = sLine.ConvertToVector(); double scalar = v1.X * v2.X + v1.Y * v2.Y; double m1 = FindMagnitude(fLine); double m2 = FindMagnitude(sLine); return(Math.Acos(scalar / m1 * m2)); }