def determ(p1, p2, p3):
    """ Helping function for convex_hull() that calculates the determinant of 3 points

        pre: p1, p2, p3 are tuples of the form (x, y) where x represents
             the x-axis location and y represents the y-axis location of the point
             on the cartesian plane
        post: returns the determinant of the three points (p1, p2, & p3)
    """

    x1, y1 = p1
    x2, y2 = p2
    x3, y3 = p3

    return (x1*y2 + x3*y1 + x2*y3 - x3*y2 - x2*y1 - x1*y3)