I总慎配大宽竖卖喊=(E-R2×0.4A)/(r+R1)=0.6AR3=(R2×0.4A)/(I总-0.4A)=30ΩP3=U3I3==(R2×0.4A)×(0.6-0.4)A=1.2W
R3=30 电功率为0.91