The parametric equations of a parabola are x=t² +1, y=2t+1.The cartesian equation of its directrix is

a) x=0 b)x+1=0 c)y=0 d) none of these

It is given that 

x = t² +1 ...(1)

y = 2t + 1 ...(2)

From (1) and (2), we get

(y – 1)² = 4 (x – 1) ...(3)

Let Y = y – 1 and  X = x – 1

Then 

(3) ⇒ Y² = 4X

Equation of the directrix for parabola Y² = 4X is:

X = –1

⇒ x – 1 = –1

⇒ x = 0

This is the required equation of directirx.

Thus, the correct answer is a.