a)\(\dfrac{1}{Rtđ}=\dfrac{1}{R1}+\dfrac{1}{R2}=\dfrac{1}{8}+\dfrac{1}{12}=\dfrac{5}{24}\)

\(\Rightarrow Rtđ=\)4,8

b)ta có:U=U1+U2=I.Rtđ=3.4,8=14,4

c)I1=\(\dfrac{U1}{R1}=\dfrac{14,4}{8}\)=1,8

I2=I-I1=3-1,8=1,2

`(15-x)+(x-12)=7-(-5+x)`

`=>15-x+x-12=7+5-x`

`=>3=12-x`

`=>x=12-3`

`=>x=9`

Vậy `x=9`

(15-x)+(x-12) = 7-(-5+x)

<=>15-x+x-12=7+5-x

<=>3=12-x

<=>x=12-3=9

(15-x)+(x-12) = 7-(-5+x)

<=> 15-x +x -12 = 7 +5 -x 

<=> x = 12 +12 -15

<=> x =9

bài V trong Review ( unit 10 - 11 -12) hả bạn?

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