Find the resistance of R
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Find the resistance of R

[From: ] [author: ] [Date: 12-02-21] [Hit: ]
I tried doing 21 ohms = 12 ohms + ((1/55ohms) + (1/x)) and solved for x.And I got 0.111 ohms for R, but I know thats not right.Im very stuck. Any help is appreciated!......
The equivalent resistance between points A and B of the resistors shown in the figure below is 21 Ω. Find the value of resistance R.

Use this diagram: http://www.webassign.net/walker/21-30.gif

I tried doing 21 ohms = 12 ohms + ((1/55ohms) + (1/x)) and solved for x.
And I got 0.111 ohms for R, but I know that's not right.

I'm very stuck. Any help is appreciated!

-
21=12+r*55/(r+55)

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The first thing is to recognize that the equivalent resistance of R in parallel with the 55Ω resistor is 9Ω.

The equivalent resistance is the inverse of the sum of the conductances.

9 = 1 / (1/R + 1/55)

1/9 = 1/R + 1/55

1/R = 1/9 - 1/55

R = 1/(1/9 - 1/55)
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