Answer
$L = \pm \frac{1}{2}$
Work Step by Step
Add $\frac{1}{L^2}$ to both sides to get $$4=\frac{1}{L^2}$$ Take the square root of both sides to get $$\sqrt{4}=\sqrt{\frac{1}{L^2}} \implies \pm 2 = \frac{1}{L}$$ Finally, take the reciprocal of both sides to get $L = \pm \frac{1}{2}$.
