# The Parametric Equations of a Parabola Are X = T2 + 1, Y = 2t + 1. the Cartesian Equation of Its Directrix is - Mathematics

MCQ

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

#### Options

• x = 0

• x + 1 = 0

• y = 0

•  none of these

#### Solution

x = 0

Given:
x = t2 + 1         (1)
y = 2t + 1         (2)
From (1) and (2):

$x = \left( \frac{y - 1}{2} \right)^2 + 1$

On simplifying: $\left( y - 1 \right)^2 = 4\left( x - 1 \right)$

Let $Y = y - 1 \text{ and } X = x - 1$

∴ $Y^2 = 4X$

Comparing it with y2 = 4ax:
= 1
Therefore, the equation of the directrix is X = −a , i.e.

$x - 1 = - 1 \Rightarrow x = 0$

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#### APPEARS IN

RD Sharma Class 11 Mathematics Textbook
Chapter 25 Parabola
Q 5 | Page 29