Question

R=1/2(r1+r2) solve for r2

Answer 1

Congrats on your first question! :) There are a few things for this problem you need to do. Are you ready?

Answer 2

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 times r2/r1+ r2 = R
:
The old "product over sum" formula for two resistors in parallel, right?

Answer 3

Did you follow that?

Answer 4

@Math.... Math is really fun once you understand it!