\({V_B} = \frac{{{Q_2}}}{{4\pi {\varepsilon _0}R}} + \frac{{{Q_1}}}{{4\pi {\varepsilon _0}\sqrt {{R^2} + {R^2}} }}\)
\({V_A} - {V_B} = \frac{{(\sqrt 2 - 1)({Q_1} - {Q_2})}}{{4\pi {\varepsilon _0}R\sqrt 2 }}\)
\(W = \frac{{q(\sqrt 2 - 1)({Q_1} - {Q_2})}}{{4\pi {\varepsilon _0}R\sqrt 2 }}\)
$\varepsilon(x)=\varepsilon_{0}+k x, \text { for }\left(0\,<\,x \leq \frac{d}{2}\right)$
$\varepsilon(x)=\varepsilon_{0}+k(d-x)$, for $\left(\frac{d}{2} \leq x \leq d\right)$