a
\(\left( E _{\text {ner }}\right)_{D}=\frac{ kq }{2 a ^{2}}+\frac{\sqrt{2 kq }}{2 a ^{2}}\)

\(\left( E _{\text {ner }}\right)_{ D }=\frac{ kq }{ a ^{2}}\left(\frac{1}{2}+\frac{1}{\sqrt{2}}\right)\)

\(\left( E _{\text {net }}\right)_{ D }=\frac{ q }{4 \pi \epsilon_{0} a ^{2}}\left(\frac{1}{2}+\frac{1}{\sqrt{2}}\right)\)