math/physics help: deriving equations for uncertainties

[alphatarget1]

i knew how to get them but my teacher is requiring us to derive it. i'm going nowhere

im trying to derive two equations: R(resistance)series=R1+R2+R3
Rparallel=(R1R2/(R1+R2))

i have the final equation but i just don't know the steps to get them. any ideas?

 

[labrat25]

uncertainties in sum = sum of uncertainties

ex. error of Rseries = sum (error R1 + error R2...)

uncertainties of multiplication (and division, same thing) is easier explained by example

given a,b (each with an uncerainty)
error of a*b = (a*b)*((error of a)/a+(error of b)/b)

i hope this makes sense... best suggestions is this from a class i took a couple years ago (Click me!)