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a,
128-3x-12=23
3x=128-12-23
3x=93
x=93:3
= 31
b,
(12x+84+55):5=35
12x+84+55=35.5
12x+84+55=175
12x=175-55-84
12x=36
x=36:12
x=3
128-3.(x+4) =23
3.(x+4) =128-23
3.(x+4) = 105
x+4 =105:3
x+4 =35
x = 35-4
x=31
a, 128 – 3(x+4) = 23
b, 12 x - 4 3 . 8 3 = 4 . 8 4
c, [(4x+28).3+55]:5 = 35
d, 720:[41 – (2x – 5)] = 2 3 . 5
a) 128 - 3(x + 4) = 23
3(x + 4) = 128 -23
3(x + 4) = 105
x + 4 = 105 : 3
x + 4 = 35
x = 35 - 4
x = 31
\(a.128-3\left(x+4\right)=23.\)
\(3\left(x+4\right)=128-23\)
\(3\left(x+4\right)=105\)
\(x+4=105:3=35\)
\(x=35-4=31\)
\(b.\left[\left(4x+28\right)\cdot3+55\right]:5=35\)
\(\left(4x+28\right)\cdot3+55=35\cdot5=175\)
\(\left(4x+28\right)\cdot3=175-55=120\)
\(4x+28=120:3=40\)
\(4x=40-28=12\)
\(x=12:4=3\)
Nếu đề là tìm x thì làm như sau :
a) 720:[41-(2x-5)]=23.5
720:[41-(2x-5)=40
41-(2x-5)=720:40
41-(2x-5)=18
2x-5=41-18
2x-5=23
2x=23+5
2x=28
x=28:2
x=14
Vậy x=14.
b) 5x+3(10-x)+x=45
5x+30-3x+x=45
5x-3x+x+30=45
3x+30=45
3x=45-30
3x=15
x=15:3
x=5
Vậy x=5.
c) |4-2x|=6
\(\Rightarrow\orbr{\begin{cases}4-2x=-6\\4-2x=6\end{cases}\Rightarrow\orbr{\begin{cases}2x=10\\2x=-2\end{cases}\Rightarrow}\orbr{\begin{cases}x=5\\x=-1\end{cases}}}\)
d) (-3)x=-27
(-3)x=(-3)3
\(\Rightarrow\)x=3
Vậy x=3
a) 720 : [41 - (2x - 5)] = 23 . 5
720 : [41 - (2x - 5)] = 8 . 5
720 : [41 - (2x - 5)] = 40
[41 - (2x - 5)] = 720 : 40
41 - (2x - 5) = 18
2x - 5 = 41 - 18
2x - 5 = 23
2x = 23 + 5
2x = 28
x = 28 : 2
x = 14
vậy x = 14
\(a,128-3.\left(x+4\right)=23\\ \Rightarrow3.\left(x+4\right)=105\\ \Rightarrow x+4=35\\ \Rightarrow x=31\\ b,\left[\left(4x+28\right).3+55\right]:5=35\\ \Rightarrow\left(4x+28\right).3+55=175\\ \Rightarrow4x+28.3=120\\ \Rightarrow4x+28=60\\ \Rightarrow4x=32\\ \Rightarrow x=8.\)
c) \(\left(12x-4^3\right).8^3=4.8^4\)
\(12x-64=4.8^4:8^3\)
\(12x-64=32\)
\(12x=32+64\)
\(12x=96\)
\(x=\dfrac{96}{12}\)
\(x=8\)
d) \(720:\left[41-\left(2x-5\right)\right]:5=35\)
\(720:\left(41-2x+5\right):5=35\)
\(720:\left(46-2x\right)=35.5\)
\(720:\left(46-2x\right)=175\)
\(46-2x=720:175\)
\(46-2x=\dfrac{144}{35}\)
\(2x=46-\dfrac{144}{35}\)
\(2x=\dfrac{1466}{35}\)
\(x=\dfrac{1466}{35}:2\)
\(x=\dfrac{733}{35}\)