Question

The length of the double ordinate of the parabola $x^2=8y$ is $8$. Then, the end points of this double ordinate are

• A. $(4,2),(4,-2)$
• B. $(2,4),(2,-4)$
• C. $(4,2),(-4,2)$
• D. $(-2,4),(2,4)$

Answer 1

Answer: (C)

The length of double ordinate of parabola $=8=PQ$
$\therefore$ $PR=RQ=4$
$\therefore$ Coordinates of P and Q will be
$(-4,y_1)$ and $(4,y_1)$ Since, P lies on $x^2=8y$
$\therefore$ ${(-4)}^2=8y_1\Rightarrow 16=8y_1\Rightarrow y_1=2$
Hence, coordinates of end points of double ordinate are (4, 2) and $(-4,2)$ .