Question

solve the problem,find series and parallel combination.

Answer 1

This one is an infinite ladder case.
Since the resistances go till infinity so we can take the net resistance to be 'X'.
Even on removal of one part there is no change in the value of X so we exclude the first 3 resistors and take the rest to be X.
Now you can solve the above and equate the value for X.
Also since X can't be negative so value of X is 6.
Hope this helps... :)