At what point on

If the tangent is parallel to y-axis it means that it’s slope is

not defined or 1/0.

2y – 4 = 0 ⇒ y = 2

x² + (2)² – 2x – 4(2) + 1 = 0

⇒ x² – 2x – 3 = 0

⇒ x = 3 and x = -1

So, the requied points are (-1, 2) and (3, 2).