Solving $L = 4\pi C_x d^2$ for $d$ I need to re-arrange the following equation to solve for $d$:
$$L = 4\pi C_x d^2$$
Thank you.

As Arturo said
$$L=4 \pi C_x d^2$$
$$\implies d^2 = \frac{L}{4 \pi C_x}$$
$$\implies d= \pm\sqrt{\frac{L}{4 \pi C_x}}$$
Your equation looks like it is physical, so the negative square root may not be relevant
