并联电阻电路的总电阻是怎么算出来的?

在n个电阻的并联电路中：设电压为U；总电阻为R,分电阻为R1、R2······Rn；总电流为I,分电流为I1、I2······In则：
I=U/R1+U/R2+······+Rn
R=U/I
=U/(U/R1+U/R2+······+U/Rn)
=1/(1/R1+1/R2+······+1/Rn)
∴1/R=1/R1+1/R2+······1/Rn
或：
I=I1+I2+······+In
U/R=U/R1+U/R2+······+U/Rn
∴1/R=1/R1+1/R2+······+1/Rn