Here we will apply superposition principle.

(i) Let us feed a current I to point 1, but do not draw the current from 2 and allow the current to spread to infinity. Then current in branch ‘12’ will be

(ii) Secondly, feed current I to the current at take it out from 2, now again current through branch ‘12’ will be

(iii) Now carry out both the above steps (i) and (ii) simultaneously. Then current in branch ‘12’ will be sum of above two currents i.e.,

Resistance between 1 and 2 is . Let remaining resistance is .

Then