串并联电路电阻,电压（电流）分配,功率分配的推导

串：
R=R1+R2 串联电路总电阻值等于各电阻值之和
R=U/I
}R=U1+U2/I }R=U1/I +U2/I =R1+R2
U=U1+U2 ∵I=I1=12
U1/U2=R1/R2
U=IR→U1/U2=I1R1/I2R2 ∵ I=I1=I2 ∴U1/U2=R1/R2
P1/P2=R1/R2
P=I²R P1/P2=I²R1/I²R2 ∵I=I1=I2 ∴ P1/P1=R1/R2
并
1/R=1/R①+1/R②
∵R=U/I
U=U1=U2
∴1/R=U/I1+I2
1/R=U/I1+U/I2
1/R=1/R①=1/R②
I1/I2=R1/R2
U=I1R1=I2R2
I1/12=R2/R1
P1/P2=R2/R1
∵P=U²/R
P1/P2=U²/R1/U²/R2=R2/R1