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I'm completely lost as to how to find the equivalent resistance of this circuit:

enter image description here

It's R6 that's causing me problems. I can't find an expression since a bunch of nodes connect to each other. Anyone got any pointers?

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    \$\begingroup\$ Convert the delta to a Y. \$\endgroup\$ – Ignacio Vazquez-Abrams Sep 23 '13 at 9:26
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    \$\begingroup\$ Actually, the problem isn't as much R6 as it is R7. If you ignore R1 and R4 for a moment, you'll see that R1, R2, R3 and R6 form a bridge, and R7 spans the bridge. This means that the influence of R7 depends on how well the bridge is balanced -- indeed, if the bridge is exactly balanced, the value of R7 has no influence on the total resistance at all. It could be anything from a dead short to an open circuit. Is that enough of a hint to get you going? \$\endgroup\$ – Dave Tweed Sep 23 '13 at 11:56
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Convert the interior Wye (R3, R7, R6) to a delta. The sides of this delta are in parallel with R1, R2 and R5.

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