Which of the following is not used in Friedel-Crafts reaction?

$A$ variable plane passes through a fixed point $(1, 2, 3)$. The foot of the perpendicular from the origin to the plane lies on:

Assertion $(A)$: $-NH_2$ group of aniline is ortho,para directing in electrophilic substitutions.
Reason $(R)$: $-NH_2$ group stabilises the arenium ion formed by the ortho,para attack of the electrophile.
The correct answer is

If $\frac{dy}{dx} = \frac{xy + y}{xy + x}$,then the solution of the differential equation is

The equation of the normal to the curve $y^4=ax^3$ at $(a, a)$ is

The angle between the pair of straight lines formed by joining the points of intersection of $x^2+y^2=4$ and $y=3x+c$ to the origin is a right angle. Then $c^2$ is equal to