At What Points On Curves X2 Y2 2x 4y 1 0 Tangents Are Parallel To Y Axis

At what points on the curves x2+y2-2x-4y+1 = 0, the tangents are parallel to the y- axis ?

Answers:

Given equation of the curve is 
x² + y² – 2x – 4y + 1 = 0 …(i)
Differentiating w.r.t.x, we get