import math
AX = 0
AY = 0
BX = 100
BY = 0

abx = AX - BX
aby = AY - BY

minangle = 100
minindex = -1

pts = [[50, -10],[50, -20],[50, 1],[50, 20]]
for i, p in enumerate(pts):
    pbx = p[0] - BX
    pby = p[1] - BY
    angle = math.atan2(-pbx*aby+pby*abx, pbx*abx+pby*aby)
    if angle < 0:
        angle += 2*math.pi
    if angle < minangle:
        minangle = angle
        minindex = i

print(pts[minindex])# your code goes here