1/r=r1+r2 ?

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Answer 1 · 2015-10-23T18:35:28

$r = \frac{r_{1} r_{2}}{r_{1} + r_{2}}$ $r = (r_1r_2)/(r_1+r_2)$
Depending on what your question means!

Assumption:
r1 -> $r_{1}$ $r_1$
r2-> $r_{2}$ $r_2$

Then we have:

$\frac{1}{r} = \frac{1}{r_{1}} + \frac{1}{r_{2}}$ $1/r = 1/(r_1) + 1/(r_2)$

giving:

$\frac{1}{r} = \frac{r_{2} + r_{1}}{r_{1} r_{2}}$ $1/r = (r_2 + r_1)/(r_1 r_2)$

To find r invert the whole equation giving:

$r = \frac{r_{1} r_{2}}{r_{1} + r_{2}}$ $r = (r_1r_2)/(r_1+r_2)$

Is this what your question means?