Calculate the equivalent resistance between A and B 
Find the equivalent resistance between A and B. 
I tried using nodal but there were too many unknown variables.
Please help.
Thank you!
 A: If you cannot see that this is a Wheatstone bridge (2:4 = 3:6, so the two "arms" are balanced and there is no current in the 5 Ohm resistor) then you can use a simple analysis with just two unknowns: the voltage at the two nodes between A and B, call them x (where 2,4,5 meet) and y (3,5,6 meet). Given an imposed voltage V at A, and 0 (ground) at B, you can now write two equations in three unknowns - namely, the sum of currents flowing out of the nodes x, y must be zero. Now the current flowing out is given by voltage difference between source (the node) and destination (where it's flowing to), so we get:
$$\frac{x-V}{2} + \frac{x-y}{5} + \frac{x}{4} = 0\\
\frac{y-V}{3} + \frac{y-x}{5} + \frac{y}{6} = 0$$
We can pick $V$ to be anything we want it to be - all we care about is the total current that flows because we're looking for the equivalent resistance.
Now $V=I\cdot R$ so $R = \frac{V}{I}$ . We can find $I$ from
$$I = \frac{V-x}{2} + \frac{V-y}{3}$$
If you just set $V=1$ then solving the above equations results in $I=R_{equivalent}$ and you're done.
Leaving that as an exercise... spotting the balanced bridge definitely saves some time.
