求内阻R: 32 a 62 + 42 U 20 b 42 a R 6.42 R=2+1.6=3.62 =33/(3.6+6.4)=3.3A 93 b求内阻Ri ： Ri =2+1.6=3.6 I=33/(3.6+6.4)=3.3A a b I0 U0 3 4 6 2 4 +  6. 4 I a b Uoc Ri + 