$\because \quad y=2 x$

or $\quad \frac{d y}{d x}=2$

$\therefore \quad \mathrm{m}_{1}=2$

$\therefore \quad \mathrm{m}_{1} \mathrm{m}_{2}=-1$

$\mathrm{m}_{2}=-\frac{1}{2}$

$\therefore$ $\tan \theta=-\frac{1}{2}$

where $\theta$ is angle with $x$ $-axis.$

$\tan \theta=\frac{4}{-8}=-\frac{1}{2}$