(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

[PLAIN]http://img441.imageshack.us/img441/7796/81673480.jpg [Broken]

given this circuit find the total resistance of the circuit

2. Relevant equations

I = V/R

3. The attempt at a solution

ok I think that there are two ways of solving this, 1 by finding the total resistance directly from the resistors because some are in series some are in parallel

the other way is to find the total current and then the Rtot will be V/Itot

So, I found the I total using the online wolframalpha calculator which is

solve[{36 - 3y - 6(y+z)=0,36-6x-3(x-z)=0,-6x-3z+3y=0},{x,y,z}]

so

x = 24/7 ~~ 3.428571 and y = 36/7 ~~ 5.142857 and z = -12/7 ~~ -1.714286

x is I1 which flows over R1 y is I2 which flows over R4 and z is I3 which flows over R3

the answers are correct since my book has the same answers for the currents

so Itot = I1 + I2 = 3.428571+5.142857 = 8.571428 A

hence Rtot = 36*Itot = 4.2 Ω (which is the correct answer)

using the method with parallel and series I said that R5 and R3 are in parallel, hence, R35 = 2 Ω

R35 is in series with R4 hence R345 = 2 + 3 = 5 Ω

R345 is in parallel with R12 = 9 Ω

SO Rtot = 45 / 14 = 3.21428571

I can't understand why im getting different results, can anyone help me? thanks

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# Homework Help: How is this possible? (circuits)

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