7 + (-12 + 43) - [2 + (19 - 34) ]

= 7 + 31 - [ 2 + (-15)]

= 38 - (-15)

= 53

 7+(-12+43)-[ 2+(19-34)]

= 7 + (-12 + 43 ) - [ 2 + ( 19 - 34 ) ]

= 7 +   32 - [ 2 + ( -15 ) ]

= 7 + 32 - ( - 13 )

= 39 - ( - 13 )

= 52

7 + (-12 + 43) - [ 2 + (19 - 37) ]

= 7 + 31 - [2 + (-15) ]

= 38 - (-13)

= 51

52 nhé 51 là sai

\(\Rightarrow7+31-\left[2+\left(-15\right)\right]\)

\(\Rightarrow7+31-\left(-13\right)=7+31+13=20+31=51\)

\(7+\left(-12+43\right)-\left[2+\left(19-34\right)\right]\)

\(=7+31-\left[2+\left(-15\right)\right]\)

\(=7+31-\left(-13\right)\)

\(=38+\left(-13\right)\)

\(=25\)

a, 25+ ( - 13 + 8 )

= 25+ ( -5 ) = 20

b, 7 + ( - 12 + 43 ) - [ 2 + (19 - 34)]

= 7 + 31 - [ 2 + ( - 15 ) ]

= 7 + 31 - ( - 13 )

= 38 - ( - 13 )

= 51

tk cho mk nha

7+(-12+ 43)- [2+(19- 34)]=7+31- [2+(-15)]

=7+31-(-13)

=38-(-13)=51

7+(-12+ 43)- [2+(19- 34)]

=7+31-[2+(-15)]

=7+31-(-13)

=38-(-13)

=51

7+(-12+ 43)- [2+(19- 34)]

=7+31-[2+(-15)]

=7+31-(-13)

=38-(-13)

=51

12536 x 6 

= 75216

k nha thiên thần trong mơ 

75216 nha bạn

12536x6=75216

\(\Rightarrow Rtd=\dfrac{Rac.Rd}{Rac+Rd}+\dfrac{Rbc.R1}{Rbc+R1}=\dfrac{12.\left(\dfrac{6^2}{6}\right)}{12+\dfrac{6^2}{6}}+\dfrac{12.12}{12+12}=10\Omega\)

\(b,\Rightarrow Ibc1=\dfrac{U}{Rtd}=\dfrac{12}{10}=1,2A\Rightarrow Ubc1=Ibc1\left(\dfrac{Rbc.R1}{Rbc+R1}\right)=7,2V\Rightarrow I1=\dfrac{7,2}{R1}=0,6A\Rightarrow Q1=I1^2R1t=1296W\)

\(c,\Rightarrow\left\{{}\begin{matrix}Ud=6V=Uac\\Id=\dfrac{Pdm}{Udm}=1A\end{matrix}\right.\)

\(\Rightarrow\)\(\dfrac{12}{Rtd}=\dfrac{12}{\dfrac{Rac.Rd}{Rac+Rd}+\dfrac{\left(24-Rac\right)R1}{24-Rac+R1}}=\dfrac{12}{\dfrac{6Rac}{6+rac}+\dfrac{\left(24-Rac\right).12}{36-Rac}}=Iacd\)

\(\Rightarrow1+Iac=Iacd\Rightarrow1+\dfrac{6}{Rac}=\dfrac{12}{\dfrac{6Rac}{6+Rac}+\dfrac{\left(24-Rac\right)12}{36-Rac}}\Rightarrow Rac=12\sqrt{2}\left(\Omega\right)\)

3. R4 nt {R1//(R2ntR3)}

\(a,\Leftrightarrow\)\(Ia=0,3A=I2=I3\Rightarrow U23=U123=I2.\left(R2+R3\right)=6V\)

\(\Rightarrow Im=\dfrac{U123}{R123}=\dfrac{6}{\dfrac{R1\left(R2+R3\right)}{R1+R2+R3}}=0,5A\Rightarrow Uab=Im.Rtd=0,5\left(R4+R123\right)=10V\)

\(b,\) R2//{R1 nt(R3//R4)}

\(\Rightarrow K\) mở \(\Rightarrow I3=\dfrac{U.R123}{Rtd.R23}=\dfrac{6}{12+R4}\left(A\right)\)

\(\Rightarrow K\) đóng \(\Rightarrow I3=\dfrac{U.R4}{R134.R34}=\dfrac{2R4}{30+7R4}\left(A\right)\)

\(\Rightarrow R4=15\Omega\)

\(\Rightarrow Ik=I2+I3=\dfrac{U}{R2}+\dfrac{2.15}{30+7.15}=\dfrac{10}{15}+\dfrac{2.15}{30+7.15}=\dfrac{8}{9}A\)