Find the length of the line-segment joining the vertex of the parabola $y^2=4ax$ and a point on the parabola where the line-segment makes an angle $\theta$ to the $x$-axis.

Question

$\begin{array}{1 1}\large\frac{2a\sin \theta}{\cos^2\theta}\\\large\frac{2a\cos \theta}{\sin^2\theta}\\\large\frac{4a\sin \theta}{\cos^2\theta}\\\large\frac{4a\cos \theta}{\sin^2\theta}\end{array}$