Question

(1/R)=(1/r)+(1/S)
find (dR/dr) if s is a constant?

Answer 1

I think i got it:

1/R = 1/r+1/s ---> 1/R = (s+r)/r*s ---> R = r*s/(s+r)

So you derive it, you take out the constant s and... use the rule for deriving f(x)/g(x)

d(r/r+x) = [ (r+s)(1) - r(1) ] / [r+s]^2

It all ends being( s^2) / [r+s]^2

What do you think?