Find the the equivalent resistance between points `A` and `B`.

Explanation

(a) Symmetry about perpendicular bisector of `AB` i.e. `XY. X` and `Y` are at same potential. Make new diagram by placing `X` and `Y` at one place and solve.

(b) Symmetery about perpendicular bisector of `AB` i.e `XYZ`, hence point `X, Y` and `Z` are at the same potential. Make new diagram by placing `X, Y` and `Z` at one place and solve.
Since the right half is mirror image of the left half, hence solve only for the left half.

( c) Symmetry about `AB`, the points `X, Y` and `Z` are at the same potential, make new diagram by placing `X, Y` and `Z` at one place and solve.
Solve only for the left half , the right half is mirror image of it.
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