B B i=0 R B 十 十 i=i A Thevenin-eguivalent-circuiti B  oc Rth A  oc Rth i B A A  oc  oc + −− + B  oc Rth A i'= 0 + −  oc B  oc Rth A i'' − +  oc − +  oc Rth Thevenin− equivalent − circuit B i = i