Infinite sequence of resistors

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1. May 27, 2016

diredragon

1. The problem statement, all variables and given/known data
From the picture below, calculate the net resistance between points A and B if
$R_1=12$
$R_2=3.75$
2. Relevant equations
3. The attempt at a solution

I cannot think of any way but to find the equivalent resistance od $R_1$ and $R_2$ and add them up but since there are infinite number of those equivalences the resistance at the end is infinity!
$R_{12}=\frac{R_1R_2}{R_1+R_2}= 2.86$
The infinite sequence od these gives inifinity so what is wrong?

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2. May 27, 2016

Staff: Mentor

Mentor Note: members are reminded that on this forum the assistance given is to take the form of hints and guidance. Complete homework solutions do not help understanding and must not be contributed.

3. May 27, 2016

Staff: Mentor

If you glance towards the foot of this page you will see links to some older PF threads which may cast light on the problem at hand.

4. May 27, 2016

Staff: Mentor

Is this a multiple choice question? If so, what are the answers to choose from?

5. May 28, 2016

diredragon

The choices are 15, 15.75, 2.86, 30, 7.5, infinity.
I found the equation $R^2 - R_1R - R_1R_2=0$ on the web and it came out with 15 so i think that is the answer

6. May 28, 2016

Staff: Mentor

You can easily check your answer. Arrange 12, 3.75 and 15 Ω resistors and see what the result is.