Three equal resistors each equal to $r$ are connected as shown in the figure. The equivalent resistance between points $A$ and $B$ is:

Calculate the equivalent resistance between $A$ and $B$.

Find the equivalent resistance across $AB$.

Each of the resistance in the net work shown in the figure is equal to $R$. The resistance between the terminals $A$ and $B$ is

In the circuit shown here, what is the value of the unknown resistor $R$, so, that the total resistance of the circuit between points $P$ and $Q$ is also equal to $R$?