Question

How to find the resistance across ab?

Answer 1

Explanation:

the answer is 2R.

here we see that if we extend the arm A containing the two 3R resistors, we see that it forms a Wheatstone bridge with 5R as the central resisitor,so the 5R is short circuited and doesn't come into picture, so we have two (3R and R) in series which are in parallel with each other.

So, answer=(3R+R)//(3R+R)= 4R//4R= 2R.