Determine the total resistance of a loop made up of equal resistances, each equal to r.

It is necessary to take one of the points from which the conductors extend to the sides for the current source and place the arrows – the direction of the current. Where two arrows meet, the charge will be zero, and we do not take these resistors into account. We also do not take into account the resistance of the resistors located on the axis of symmetry. The remaining resistors must be counted and multiplied by the resistance r. It will turn out to be 4r.