V2=-6
V4= 12
V3+12=V1 ......(1)
V3/2K+(V3-V2)/1K+(V3-V4)/1K +(V1-V2)/2k+ (V1-V4)/2k=0
----> V3/2K+(V3+6)/1K+(V3-12)/1K+(V1+6)2K +(V1-12)/2k=0
---->V3 + 2V3+12 +2V3-24 +V1+6 +V1-12=0
-----> 5V3 +2V1 =8........(2)
联立 (1)(2)解得:V3=-16/7
所以 Io= V3/2K= -16/14K= -8/7 mA