Question 12
The equations of $L_1$ and $L_2$ are $y=mx$ and $y=nx,$ respectively. Suppose $L_1$ makes twice as large an angle with the horizontal (measured counterclockwise from the positive $x$-axis) as does $L_2,$ and that $L_1$ has $4$ times the slope of $L_2.$ If $L_1$ is not horizontal, then $mn$ is