b) 25 -2x =27
2x =27-25
2x= 2
x= 2:2
x=1
Vậy...
Câu 1 thiếu đề r bn
b, 25 - 2x = 27
=) 2x = 25 - 27 = -2
=) x = -2 : 2 = -1
c) 29 -x = -30
x= 29 -( -30)
x= 59
Vậy....
c, 29 -x = -30
=) x = 29 - ( - 30 ) = 29 + 30 = 59
=) x = 59
d) 4x - 45 = 17
4x =17+45
4x= 62
x= 62:4
x= 31/2
Vậy...
Đề sai sai
d, 4x - 45 = 17
=) 4x = 17 + 45 = 62
=) x = 62 : 4 = 13
e) 12 - ( 30 - x) = -23
30-x= 12-(-23)
30-x =35
x= 30 -35
x= -5
Vậy..
e, 12 - ( 30 - x) = -23
=) 30 - x = 12-(-23) 35
=) X = 30 - 35 = -5
f) | x - 7 | + 15 = 28
| x - 7 | = 28 -15
| x - 7 | =13
TH1; x-7 =13
x= 13+7
x= 20
TH2: x - 7 = -13
x= -13+7
x= -6
Vậy...
f, | x - 7 | + 15 = 28
=) | x - 7 | = 28 - 15 = 13
=) 2th
TH1 : x-7 = 13 =) x= 13 + 7 = 20
TH2 : x-7 = -13 =) x = -13 + 7 = -6
vậy x \(\in\){ -6 ; 20 }
Câu a sai đề
b) \(25-2x=27\Leftrightarrow2x=25-27=-2\Leftrightarrow x=\left(-2\right)\div2=-1\)
c) \(29-x=-30\Leftrightarrow x=29-\left(-30\right)=29+30=59\)
d) \(4x-45=17\Leftrightarrow4x=45+17=68\Leftrightarrow x=68\div4=17\)
e) \(12-\left(30-x\right)=-23\Leftrightarrow30-x=12-\left(-23\right)=12+23=35\)
\(\Leftrightarrow30-x=35\Leftrightarrow x=30-35\Leftrightarrow x=-5\)
f) \(|x-7|+15=28\Leftrightarrow|x-7|=28-15=13\) . Xét 2 trường hợp :
\(x-7=13\Rightarrow x=13+7=20\) ; \(x-7=-13\Rightarrow x=\left(-13\right)+7=-6\)