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a) 2 . x + 12 = 36
2 . x = 36 - 12
2 . x = 24
x = 24 : 2
x = 12
Vậy x = 12
b) (x + 21) : 8 + 12 = 21
( x + 21 ) : 8 = 21 - 12
( x + 21 ) : 8 = 9
x + 21 = 9 . 8
x + 21 = 72
x = 72 - 21
x = 51
Vậy x = 51
c) (3 . x - 18) . (x - 9) = 0
\(\Rightarrow\begin{cases}3.x-18=0\\x-9=0\end{cases}\)
\(\Rightarrow\begin{cases}3.x=18\\x=0+9\end{cases}\)
\(\Rightarrow\begin{cases}x=18:3=6\\x=9\end{cases}\)
Vậy \(x\in\left\{6;9\right\}\)
a)
\(2x+12=36\)
\(\Rightarrow2\left(x+6\right)=36\)
\(\Rightarrow x+6=18\)
=> x = 12
Vậy x = 12
b)
\(\left(x+21\right):8+12=21\)
\(\Rightarrow\left(x+21\right):8=9\)
\(\Rightarrow x+21=72\)
=> x = 51
Vậy x = 51
c)
\(\left(3x-18\right)\left(x-9\right)=0\)
\(\Rightarrow3\left(x-6\right)\left(x-9\right)=0\)
\(\Rightarrow\left(x-6\right)\left(x-9\right)=0\)
\(\Rightarrow\left[\begin{array}{nghiempt}x-6=0\\x-9=0\end{array}\right.\)
\(\Rightarrow\left[\begin{array}{nghiempt}x=6\\x=9\end{array}\right.\)
Vậy x = 6 ; x = 9
Bài 2 : a, x = -36/9 = -4
b, đề sai
c, <=> -2 =< x =< -3 => x = -1
Bài 1:
a: 2/8=9/36; 2/9=8/36; 8/2=36/9; 9/2=36/8
b: -2/4=9/-18; -2/9=4/-18; 4/-2=-18/9; 9/-2=-18/4
Bài 2:
a: =>x/3=-4/3
hay x=-4
Câu b đề sai rồi bạn
`a)`
`x-15 = -21`
`<=> x = -21 + 15`
`<=> x = -6`
`b)`
`42 - x = -7`
`<=> x = 42 - (-7)`
`<=> x = 42 + 7`
`<=> x = 49`
`c)`
`12 - (30-x) = -23`
`30-x = 12 - (-23)`
`30-x = 35`
`x = 30-35`
`x = -5`
`d)`
`31 - (17+x)=18`
`<=> 17+x = 31-18`
`<=> 17+x =13`
`<=> x = 13-17`
`<=> x = -4`
a) \(x-15=-21\)
\(\Rightarrow x=-21+15=-6\)
b) \(42-x=-7\)
\(\Rightarrow x=42+7=49\)
c) \(12-\left(30-x\right)=-23\)
\(\Rightarrow30-x=12+23=35\)
\(\Rightarrow x=30+35=65\)
d) \(31-\left(17+x\right)=18\)
\(\Rightarrow17+x=31-18=13\)
\(\Rightarrow x=13-17=-4\)
1) 5.( x - 6 ) - 2.( x + 9 ) = 21
5x - 30 - 2x - 18 = 21
3x - 48 = 21
3x = 21 + 48
3x = 69
x = 23
2) 2.( x + 3 ) + 3.( x + 1 ) = 15 - ( - 9 )
2x + 6 + 3x + 3 = 24
5x + 9 = 24
5x = 24 - 9
5x = 15
x = 3
3) ( - x + 5 ).(3 - x ) = 0
=> - x + 5 = 0 hoặc 3 - x = 0
=> x = 5 hoặc x = 3
4) ( x - 12 ) - 15 = ( 20 - 7 ) - ( 18 + x )
x - 12 - 15 = 13 - 18 - x
x - 27 = - 5 - x
x + x = - 5 + 27
2x = 22
x = 11
5) x - ( 17 - 8 ) = 5 + ( 10 - 3x )
x - 9 = 5 + 10 - 3x
x + 3x = 15 + 9
4x = 24
x = 6
a: \(\Leftrightarrow\dfrac{x}{-4}=\dfrac{21}{y}=\dfrac{z}{-80}=\dfrac{3}{4}\)
=>x=-3; y=28; z=-60
b: 5/12=x/-72
=>x=-72*5/12=-6*5=-30
c: =>x+3=-5
=>x=-8
\(a,x+7=5-14\)
\(x+7=-9\)
\(x=-9-7\)
\(x=-16\)
\(b,-18-x=-8-13\)
\(-18-x=-21\)
\(x=-18+21\)
\(x=3\)
\(c,311-x+82=46+\left(x-21\right)\)
\(393-x=46+x-21\)
\(393-x=25+x\)
\(x+x=393-25\)
\(2x=368\)
\(x=184\)
\(d,\left|x-8\right|=7\)
\(\Rightarrow\orbr{\begin{cases}x-8=7\\x-8=-7\end{cases}\Rightarrow\orbr{\begin{cases}x=15\\x=1\end{cases}}}\)
\(f,12-x=25-\left(-7\right)\)
\(12-x=25+7\)
\(12-x=32\)
\(x=12-32\)
\(x=-20\)
\(g,-20+x=11-\left(-12\right)\)
\(-20+x=11+12\)
\(-20+x=23\)
\(x=23+20\)
\(x=43\)
\(h,-x-15=\left(-4\right)-\left(27-20\right)\)
\(-x-15=-11\)
\(x=-15+11\)
\(x=-4\)
\(i,15-\left(x-7\right)=-21\)
\(15-x+7=-21\)
\(22-x=-21\)
\(x=22+21\)
\(x=43\)
\(k,\left|x-3\right|+8=7\)
\(\left|x-3\right|=7-8\)
\(\left|x-3\right|=-1\)
\(TH1:x-3\ge0\Leftrightarrow x\ge3\)
\(\Rightarrow x-3=-1\)
\(\Rightarrow x=2\)( loại )
\(TH2:x-3< 0\Leftrightarrow x< 3\)
\(\Rightarrow-x+3=-1\)
\(\Rightarrow x=4\)( loại )
=> ko có giá trị nào cả
\(l,\left(x-2\right)\times\left(x+15\right)=0\)
\(\Rightarrow\orbr{\begin{cases}x-2=0\\x+15=0\end{cases}\Rightarrow\orbr{\begin{cases}x=2\\x=-15\end{cases}}}\)
\(m,-6x-\left(-7\right)=25\)
\(-6x+7=25\)
\(-6x=25-7\)
\(-6x=18\)
\(x=-3\)
a)\(x-15=3\Leftrightarrow x=3+15\Leftrightarrow x=18\)
b) \(2x+12=36\Leftrightarrow2x=24\Leftrightarrow x=12\)
c)\(\left(x+21\right):8+12=21\)
\(\Leftrightarrow\)\(\frac{x+21}{8}=9\)
\(\Leftrightarrow x+21=72\)
\(\Leftrightarrow x=51\)
d)\(\left(3x+18\right)\left(x-9\right)=0\)
\(\Leftrightarrow\left[\begin{array}{nghiempt}3x-18=0\\x-9=0\end{array}\right.\)
\(\Leftrightarrow\left[\begin{array}{nghiempt}x=6\\x=9\end{array}\right.\)