1/R总 =1/R1+1/R2+...+1/RN
1/R1+1/R2+1/R3+```````````1/Rn=1/R总 或(R1R2R3R4````Rn)/(R1+R2+R3+``````+Rn)=R总
1/R1+1/R2=1/R总
1/R1+1/R2+```````+1/rn=1/R总