def find_cross(ln1, ln2):
    """
    finds cross points of 2 lines. Lines are defined as (a,b): ax+by=1
    :param ln1:
    :param ln2:
    :return: (x,y)
    """
    d = ln1[0]*ln2[1] - ln2[0]*ln1[1]
    return (ln2[1]-ln1[1])/d, (ln1[0]-ln2[0])/d