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Solving a literal equation containing fractions.

1/R=(1/R1)+(1/R2) solve for R1. I can't figure out what to do, I always end up where I have to either get rid of R1 or an answer that doesn't work when plugging it back in.

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marked as duplicate by MJD, Chris Eagle, t.b., sdcvvc, J. M. Aug 29 '12 at 10:35

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2 Answers 2

Hint:

1) isolate 1/R1

2) simplify both sides of that isolation

3) figure out the two conditions for this to work

If this is not clear, ask again.

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$$ \frac{1}{R}= \frac{1}{R_1} +\frac{1}{R_2} $$

$$ \frac{1}{R_1}=\frac{1}{R}-\frac{1}{R_2} $$

$$ R_1=\frac{1}{\frac{1}{R}-\frac{1}{R_2}} = \frac{1}{\frac{R_2-R}{R\, R_2}}= \frac{R\, R_2}{R_2-R} . $$

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Thank you for showing me how to get to the answer because the book I'm using did not give me the answer to the question so I was not sure if any of the answers I got were right. –  Dragoon2375 Aug 27 '12 at 4:10

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