(1)由P=UI得,I1=P/U1=3W/6V=0.5A
I2=I1=0.5A
U2=U-U1=15V-6V=9V
R2=U2/I2=9V/0.5A=18Ω
P总=U总I总=15V×0.5A=7.5W
(2)P=UI=U²/R得
R1=U²/P=(6V)²/3W=12Ω
R总=R1+R2=12Ω+48Ω=60Ω
I总=U总/R总=15V/60Ω=0.4A
I1=12=1总=0.4A
P1=U1I1=I1²R=(0.4A)²×12Ω=1.92W
P2=I2²R2==(0.4A)²×48Ω=7.68W