Three charges $Q, +q$ and $+q$ are placed at the vertices of a right -angle isosceles triangle as shown below. The net electrostatic energy of the configuration is zero, if the value of $Q$ is
JEE MAIN 2019, Diffcult
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$\mathrm{U}_{\text {Total }}=\frac{\mathrm{kQq}}{\mathrm{a}}+\frac{\mathrm{kq}^{2}}{\mathrm{a}}+\frac{\mathrm{kQq}}{\mathrm{a} \sqrt{2}}=0$
$\Rightarrow Q=\frac{-q}{\left(1+\frac{1}{\sqrt{2}}\right)}$
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