Three charges Q, +q and +q are placed at the vertices of a right angle triangle (isosceles triangle) as shown. The net electrostatic energy of the configuration is zero, if Q is equal to :

$\frac{-2q}{2+\sqrt{2}}$

Net electrostatic energy of the configuration will be

$U = K\left[\frac{q . q}{a}+\frac{Q . q}{\sqrt{2 a}}+\frac{Q . q}{a}\right]$

Here, K = $\frac{1}{4 \pi \varepsilon_0}$

$Q =\frac{-2 q}{2+\sqrt{2}}$