x - 7 = 15 - (-21)
x - 7 = 36
x = 36 + 7
x = 43
b) 3x + 17 = 2
3x = 2 - 17
3x = -15
x = -5
c) ( x - 9) = 45 - ( -35)
x - 9 = 80
x = 80 + 9
x = 89
a/ \(15-\left(x-7\right)=-21\)
\(15-x+7=-21\)
\(x=15-\left[\left(-21\right)-7\right]=15-\left(-28\right)=43\)
b/\(3x+17=2\)
\(3x=2-17=-15\)
\(x=-\frac{15}{3}=-5\)
c/\(45-\left(x-9\right)=-35\)
\(45-x+9=-35\)
\(x=45-\left[\left(-35\right)-9\right]=89\)
d/\(\left(-5\right)+x=15\)
\(x=15-\left(-5\right)=20\)
e/\(2x-\left(-17\right)=15\)
\(2x=15-17=-2\)
\(x=-\frac{2}{2}=-1\)
g/ \(Ix-2I=3\)
TH1: \(x-2=3\)
\(x=3+2=5\)
TH2: \(x-2=-3\)
\(x=\left(-3\right)+2=-1\)
=> \(x\in\left\{-1;5\right\}\)
giải:
a) 15 - ( x - 7 ) = -21
x - 7 = 15 - ( -21 ) = 36
x = 36 + 7
x = 43
b) 3x + 17 = 2
3x = 2 - 17 = -15
x = -15 : 3
x = -5
c) 45 - ( x - 9 ) = -35
x - 9 = 45 - ( -35 ) = 80
x = 80 + 9
x = 89
d) ( -5 ) + x = 15
x = 15 - (-5 )
x = 20
e) 2x - ( -17 ) = 15
2x = 15 + ( -17 ) = -2
x = -2 : 2
x = -1
g) | x - 2 | = 3
ta có 2 trường hợp
TH1 : x - 2 = 3
x = 3 + 2
x = 5
TH2: x - 2 = -3
x = -3 + 2
x = -1
vậy x = { -1;5}
a) 15 - (x -7 ) = -21
x-7=36
x=43
b) 3x+ 17 = 2
3x=-15
x=-5
c) 45 - ( x - 9 ) = -35
x-9=80
x=89
d) (-5) + x = 15
x=15-(-5)
x=20
e) 2x - ( - 17 ) = 15
2x+17=15
2x=-2
x=-1
g) |x - 2 | = 3
=>x-2=3 hoặc -3
=>x=5 hoặc -1
x - 7 = 15 - (-21)
x - 7 = 36
x = 36 + 7
x = 43
b) 3x + 17 = 2
3x = 2 - 17
3x = -15
x = -5
c) ( x - 9) = 45 - ( -35)
x - 9 = 80
x = 80 + 9
x = 89