Question 67461
{{{1/R =1/R1 + 1/R2}}}
:
Get rid of the denominators; multiply thru by (R*R1*R2), resulting in:
R1*R2 = R*R2 + R*R1
:
Factor out R on the right:
R1*R2 = R(R2 + R1)
:
Divide both sides by (R2 + R1)
{{{(R1*R2)/(R2 + R1)}}} = R
:
The old "product over sum" formula for two resistors in parallel, right?