By symmetry, currents i1 and i2 from A is the same as i1 and i2 reaching B As the same current is flowing from A to O and O to B,O can be treated as detached from AB Now CO and OD will be in series hence its total resistance =2Ω It is in parallel with CD so equivalent resistance =
2×1
2+1
=
2
3
Ω This equivalent resistance is in series with AC and DB. So total resistance =
2
3
+1+1=
8
3
Ω Now
8
3
Ω is parallel to AB that is 2Ω. So total resistance =