Question

Two charge q and -3q are placed fixed on X-axis seperated by distance d. where should a third charge 2q be placed such that it will not experience any force?

Answer 1

$KQ 2Q/x^{2} = K(3Q)(2Q)/(d+x) {2}  \\\\1/x^{2} =3/(d+x)^{2} \\\\(d+x)^{2} = 3x^{2}  \\\\x= d/\sqrt{3} -1$