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# Math formulas solve for r?

I=2V/R+2r

### 3 Answers

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- mizooLv 77 years agoFavorite Answer
I = (2V/R) + 2r

I - (2V/R) = 2r

r = (1/2) * [I - (2V/R)]

r = (I/2) - (V/R)

But if you meant to write I = 2V / (R+2r),

I * (R + 2r) = 2V

IR + 2rI = 2V

2rI = 2V - IR

r = (2V - IR) / 2I

r = (V/I) - (R/2)

- billrussell42Lv 77 years ago
ambiguous, I'll assume this is

I = (2V/R) + 2r

I'll also assume R is not the same as r

2r = I – (2V/R)

r = (I/2) – (V/R)

of course it could be

I = 2V/(R + 2r)

I(R + 2r) = 2V

R + 2r = (2V / I)

2r = (2V / I) – R

r = (V/ I) – (R/2)

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