DotProduct.cs

        /// <summary>
        /// Return DotProduct of two Vector
        /// </summary>
        /// <param name="vector"></param>
        /// <param name="other"></param>
        /// <returns></returns>
        public static double Dot(Autodesk.DesignScript.Geometry.Vector vector,
            Autodesk.DesignScript.Geometry.Vector other)
        {
            return vector.X * other.X + vector.Y * other.Y + vector.Z * other.Z;
        }

DotProduct2.cs

        /// <summary>
        /// Obtains the dot product of two vectors.
        /// </summary>
        /// <param name="u">Vector3.</param>
        /// <param name="v">Vector3.</param>
        /// <returns>The dot product.</returns>
        public static double DotProduct(this XYZ u, XYZ v)
        {
            return u.X * v.X + u.Y * v.Y + u.Z * v.Z;
        }