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

a) \(2x+12=36\Leftrightarrow2x=24x\Leftrightarrow x=12\)

b) \(x+21:8+12=21\)

\(\Leftrightarrow\frac{x+21}{8}=9\)

\(\Leftrightarrow x+21=72\)

\(\Leftrightarrow x=51\)

c) \(\left(3.x-18\right).\left(x-9\right)=0\)

\(\Leftrightarrow\left[\begin{array}{nghiempt}3x-18=0\\x-9=0\end{array}\right.\)

\(\Leftrightarrow\left[\begin{array}{nghiempt}x=6\\x=9\end{array}\right.\)

Chúc bạn học tốt 

\(43+\left(9-21\right)=317\left(x+317\right)\)

\(\Rightarrow317-\left(x+317\right)=43+\left(9-21\right)\)

\(\Rightarrow317-\left(x+317\right)=43+\left(-12\right)\)

\(\Rightarrow317-\left(x+317\right)=31\)

\(\Rightarrow x+317=317-31\)

\(\Rightarrow x+317=286\)

\(\Rightarrow x=286-317\)

\(\Rightarrow x=-31\)

Vay x = -31

\(b.\left(15-x\right)+\left(x-12\right)=7-\left(-5+x\right)\)

\(\Rightarrow15-x+x-12=7+5+x\)

\(\Rightarrow15-12=12-x\)

\(\Rightarrow3=12-x\)

\(\Rightarrow12-x=3\)

\(\Rightarrow x=12-3\)

\(\Rightarrow x=9\)

Vay x = 9 

....

a) 43+(9-21) = 317-(x+317)

43+(-12) = 317-(x+317)

317-(x+317) = 31

x+317 = 317-31=286

x = 286-317=(-31)

Tạm thời câu b mình chưa nghĩ ra nha.

a) \(43+\left(9-21\right)=317-\left(x+317\right)\)

\(43+\left(-12\right)=317-\left(x+317\right)\)

   \(317-\left(x+317\right)=31\)

\(x+317=317-31=286\)

\(x=286-317=-31\)

b) \(\left(15-x\right)+\left(x-12\right)=7-\left(-5+x\right)\)

\(15-x+x-12=7+5-x\)

\(7+5-x=\left(15-12\right)+\left(-x+x\right)\)

\(7+5-x=3+0=3\)

\(5-x=3-7=-4\)

\(x=5-\left(-4\right)=5+4=9\)

a) -12 + ( -9 + x ) = 0

              ( -9 + x ) = 0 + 12

              ( -9 + x ) = 12

                        x   = 12 + 9

                        x   = 21

Vậy x = 21

b) 21 + ( 25 - x ) = 2

             ( 25 - x ) = 2 - 21

             ( 25 - x ) = -19

                      x    = 25 + 19

                      x    = 44

Vậy x = 44

c) 461 + ( x - 45 ) = 387

              ( x - 45 ) = 387 - 461

              ( x - 45 ) = -74

                 x         = - 74 + 45

                  x         = -29 

Vậy x = -29

a, => -12-9+x = 0

=> x-21 = 0

=> x=0+21 = 21

b, => 21+25-x = 2

=> 46-x = 2

=> x = 46-2 = 44

c, => 461+x-45 = 387

=> 416+x = 387

=> x = 387 - 416 = -29

Tk mk nha

a) -12 + (-9 +x) =0

=> -21 +x =0

=> x=21

b) 21+(25-x)=2

=> 46 -x =2

=> x= 44

c) 461 + (x- 45 ) =387

=> x- 416 = 387 

=> x=    803

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)\(\left(3x+18\right)\left(x-9\right)=0\)

\(\Leftrightarrow\left[\begin{array}{nghiempt}3x-18=0\\x-9=0\end{array}\right.\)

\(\Leftrightarrow\left[\begin{array}{nghiempt}x=6\\x=9\end{array}\right.\)

Bài 9:

Ta có: \(\dfrac{12}{-6}=\dfrac{x}{5}=\dfrac{-y}{3}=\dfrac{z}{-17}=\dfrac{-t}{-9}\)

\(\Leftrightarrow\dfrac{x}{5}=\dfrac{-y}{3}=\dfrac{-z}{17}=\dfrac{t}{9}=-2\)

\(\Leftrightarrow\left\{{}\begin{matrix}\dfrac{x}{5}=-2\\\dfrac{-y}{3}=-2\\\dfrac{-z}{17}=-2\\\dfrac{t}{9}=-2\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=-10\\-y=-6\\-z=-34\\t=-18\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=-10\\y=6\\z=34\\t=-18\end{matrix}\right.\)

Vậy: (x,y,z,t)=(-10;6;34;-18)

Bài 11:

Ta có: \(\dfrac{-7}{6}=\dfrac{x}{18}=\dfrac{-98}{y}=\dfrac{-14}{z}=\dfrac{t}{102}=\dfrac{u}{-78}\)

\(\Leftrightarrow\dfrac{x}{18}=\dfrac{-98}{y}=\dfrac{-14}{z}=\dfrac{t}{102}=\dfrac{u}{-78}=\dfrac{-7}{6}\)

Ta có: \(\dfrac{x}{18}=\dfrac{-7}{6}\)

\(\Leftrightarrow x=\dfrac{18\cdot\left(-7\right)}{6}=-21\)

Ta có: \(\dfrac{-98}{y}=\dfrac{-7}{6}\)

\(\Leftrightarrow y=\dfrac{-98\cdot6}{-7}=84\)

Ta có: \(\dfrac{-14}{z}=\dfrac{-7}{6}\)

\(\Leftrightarrow z=\dfrac{-14\cdot6}{-7}=12\)

Ta có: \(\dfrac{u}{-78}=\dfrac{-7}{6}\)

\(\Leftrightarrow u=\dfrac{-78\cdot\left(-7\right)}{6}=\dfrac{78\cdot7}{6}=91\)

Ta có: \(\dfrac{t}{102}=\dfrac{-7}{6}\)

\(\Leftrightarrow t=\dfrac{-7\cdot102}{6}=-7\cdot17=-119\)

Vậy: (x,y,z,t,u)=(-21;84;12;-119;91)

Nguyễn Lê Phước Thịnh giải giùm mk bài 10 đc ko ạ

X + 6 = 12

X = 12 − 6

X = 6

14 + x = 31

X = 31 − 14

X = 17

9 + x = 61

X = 61 − 9

X = 52