CrossProduct.cs

        /// <summary>
        /// Cross Product Vector
        /// </summary>
        /// <param name="vector"></param>
        /// <param name="other"></param>
        /// <returns></returns>
        public static Autodesk.DesignScript.Geometry.Vector Cross(Autodesk.DesignScript.Geometry.Vector vector,
            Autodesk.DesignScript.Geometry.Vector other)
        {
            var x = vector.Y * other.Z - vector.Z * other.Y;
            var y = vector.Z * other.X - vector.X * other.Z;
            var z = vector.X * other.Y - vector.Y * other.X;
            Autodesk.DesignScript.Geometry.Vector v = Autodesk.DesignScript.Geometry.Vector.ByCoordinates(x, y, z);
            return v;
        }

CrossProduct2.cs

        /// <summary>
        /// Obtains the cross product of two vectors.
        /// </summary>
        /// <param name="u">Vector3.</param>
        /// <param name="v">Vector3.</param>
        /// <returns>Vector3.</returns>
        public static XYZ CrossProduct(this XYZ u, XYZ v)
        {
            double a = u.Y * v.Z - u.Z * v.Y;
            double b = u.Z * v.X - u.X * v.Z;
            double c = u.X * v.Y - u.Y * v.X;
            return new XYZ(a, b, c);
        }