R1电压U1=8*0.75=6v路端电压U=6+5=11v所以内电压1v电流I=1W/1v=1AR2电流I2=1A-0.75A=0.25AR2=6v/0.25A=24欧R4=4v/1A=4欧R3+R4=5v/1A=5欧R3=1欧
