We were given a "black box" with four terminals sticking out of the top, and told to take the voltmeter and do a set of readings for each combination of terminals. 6 combinations total, and they are listed below:

Segment Resistance(Ω)

AB 500

AC 500

AD 11.4

BC 11.4

BC 499

DC 499

Then, the instructions are to find 6 equations that will give you the internal resistors. I have found 4 of those:

1/Rab= (1/AB ) + (1/ BC+CD+AD)

1/Rbc= (1/BC) + (1/ CD+AD+AB)

1/Rcd= (1/CD ) + (1/AD+AB+BC)

1/Rad= (1/AD ) + (1/ AB+BC+CD)

Now, I can't seem to figure out the last two? A classmate said that the last two had to do with if the arrangement inside is somehow diagonal. I don't understand how to get it from there.