(A) : The locus of the point of intersection of perpendicular tangents to y² = 4ax is its directrix 

(R):If $\mathrm{\theta }$ is the angle between the pair of tangents draw from $(x_1,y_1)$ to parabola  S = 0 then tan$\mathrm{\theta }$ = $\frac{\sqrt{{\mathrm{S}}_{11}}}{\left(x_1+\mathrm{a}\right)}$