x_a = -4 (slider from -6 to 6)
y_a = 2 (slider from -4 to 2)
x_b = 6 (slider from -6 to 6)
y_b = -1 (slider from -4 to 2)
A: (x_a, y_a)
B: (x_b, y_b)
f = Line(A, B)