Question

The order of differential equations of all parabolas having directrix parallel to the $x$-axis is

• A. $3$
• B. $1$
• C. $4$
• D. $2$

Answer 1

The correct option is A

$3$

Explanation for the correct option

The equation of the parabola having directrix parallel to the $x$ axis is ${\left(x-h\right)}^2=\pm 4a\left(y-k\right)$

There are $3$ arbitrary constants $h,k$ and $a$

So the order of the differential equation is $3$

Hence, the correct option is $\left(\mathrm{A}\right)$.