Correct Answer - ` a = /(a + sqrt 2)`, the equilibrium will be stable .
.
`vec F_C = vec F_(CA) + vec F_(CB) =0 rArr F_(CA) = F_(CB)`
`K ( 2 q. Q)/ (( l + x)^2) = ( K.qQ)/x^2`
` x= ( sqrt q)/( sqrt 2q - sqrt q) l = ( sqrt 1)/( sqrt 2-1) l= ( sqrt 2 + 1) l`
Equilibrium will be stable .