explain ideas 20 and 21 while solving question 19

idea 20: Node-merging method: if two nodes have equal potential (e.g. due to symmetry), they can be short-circuited. idea 21: Edge-splitting method: a resistor between nodes A and B can be represented as a parallel connection of two resistors, and the node A can be split into two nodes, if the potentials of the new nodes A' and A' ' will be equal. These ideas are illustrated with the following problem. An hexagon ABCDEF with six \"spokes\" (connect- ing its centre 0 with the vertices) is made of 12 pieces of wire, each having a electrical resistance R. Find the resistance between the vertices A and 0 using methods '20 and 21