code: def triangle_normal(tri):
      
      vec1 = vector_generate(tri.vertices[0].data, tri.vertices[1].data)
      vec2 = vector_generate(tri.vertices[1].data, tri.vertices[2].data)
      return vector_cross(vec1, vec2)
docs: Computes the (approximate) normal vector of the input triangle.
  
      :param tri: triangle object
      :type tri: elements.Triangle
      :return: normal vector of the triangle
      :rtype: tuple