![](https://forum.eduzhixin.com/uploadfiles/20170316/1489595072356d236e67bc164f996464c7db921554.png)
![](https://forum.eduzhixin.com/uploadfiles/20170316/1489595082f286c348d35efce121a7084e2205b110.png)
首先,左上角的两个电阻被短路了,其次,剩余的三个电阻在a,b之间各自都有单独的回路,因此为1/3 *r