∵Uceq=Vcc-IcRc=12-IcRc=4 V∴Ic=(12-4)/2K=2mA∵Ic=βIb，∴Ib=2/β=0.04mA根据欧姆定律，忽略Ubb，Rb=Ucc/Ib=12/0.04=300 K
