Thread: Resistance produced by three conductors

I’m not sure how to start this problem (See attachment). I have to differentiate R with respect to R1 but the equation given is in the form 1/R, not R. How should I rearrange this function to make R the subject of this equation.

Any help showing working would be a great help.

Thanks, Daddy_Long_Legs

I think if R=1/R1+1/R2+1/R3, the 1/R=1/(1/R1+1/R2+1/R3).

1/r = 1/r1 + 1/r2 + 1/r3

1/r = {(r1 r2) + (r1 r3) + (r1 r2)} / {r1 r2 r3}

r = ...

So R would equal 1/{(r1 r2) + (r1 r3) + (r1 r2)} / {r1 r2 r3}?

Yes, and 1/{(r1 r2) + (r1 r3) + (r1 r2)} / {r1 r2 r3} will be equal to {r1 r2 r3} / {(r1 r2) + (r1 r3) + (r1 r2)}

Thanks songoku,

I just wasn't too sure of my algebra. I should be able to finish the problem.

You're welcome ^^