因为并联电路中u=u1=u2,I=I1+I2,所以U/R=U1/R1+U2/R2,即1/R=1/R1+1/R2
U=U1=U2,I=I1+I2,所以U/R=I=I1+I2=U/R1+U/R2,即1/R=1/R1+1/R2
