z_1+z_2

z_2-z_4

z_3z_3

z_2z_4

z_2/z_4

C = Intersect(xAxis, yAxis)
c = Circle(C, 1)
z_2 = (1, 1)
z_1 = (2, 0)
z_4 = (0, -1)
z_3 = (-0.5, 0.8660254037844386)
v_2 = Vector(C, z_2)
v_1 = Vector(C, z_1)
v_3 = Vector(C, z_3)
v_4 = Vector(C, z_4)