若1/R=1/R1+1/R2,则.A:R=R1+R2,B:R=R1+R2/R1+R2,C:R=R1R2/R2+R1,D:R=R1R2/R1-R2求大神帮助/是除号

问题描述:

若1/R=1/R1+1/R2,则.A:R=R1+R2,B:R=R1+R2/R1+R2,C:R=R1R2/R2+R1,D:R=R1R2/R1-R2求大神帮助
/是除号

本题选择C。因为:1/R=1/R1+1/R2,两边同时乘以R,得:1=R/R1+R/R2,通分,即:1=R(R1+R2)/R1R2,所以,R=R1R2/(R2+R1) ,选C

C:R=R1R2/(R2+R1)