\(F=\frac{G m^2}{a^2} \text { and } F^{\prime}=\frac{G m^2}{(\sqrt{2} a)^2}\)
\(F_{\text {net }}=\sqrt{2} \frac{G m^2}{a^2}+\frac{G m^2}{2 a^2}\)
\(\left(\frac{2 \sqrt{2}+1}{32}\right) \frac{G m^2}{L^2}=\frac{G m^2}{a^2}\left(\frac{2 \sqrt{2}+1}{2}\right)\)
\(a=4 L\)