The network is given in Fig. (a)
Its equivalent circuit is given in Fig. (b)
It is a balanced Wheatstone bridge in which resistance R between P and Q carries no current. Hence we have effective circuit as shown in Fig. (c).
Terminals A and B have two resistances of values 2R in parallel.
Hence, total resistance
RT = \(\frac{2R\times2R}{2R+2R}\) = R
