Phanh đã chuyển đến đây 

1/2 . x + 3/5 . (x-2) = 3

1/2 . x + 3/5 . x - 3/5 . 2 = 3

1/2 . x + 3/5 . x - 6/5 = 3

x.(1/2+3/5) - 6/5 = 3

x.11/10 - 6/5 = 3

x.11/10 =3+6/5

x.11/10 =21/5

x = 21/5:11/10

x =42/11 

này làm gì thế,nghĩa là sao

\(5\cdot x+10\cdot9=990\)

\(\Rightarrow5\cdot x+90=990\)

\(\Rightarrow5\cdot x=900\)

\(\Rightarrow x=\dfrac{900}{5}\)

\(\Rightarrow x=180\)

_____________

\(1045:\left[215-\left(3\cdot x-24\right)\right]=5\)

\(\Rightarrow215-\left(3\cdot x-24\right)=1045:5\)

\(\Rightarrow215-\left(3\cdot x-24\right)=209\)

\(\Rightarrow3\cdot x-24=215-209\)

\(\Rightarrow3\cdot x-24=6\)

\(\Rightarrow3\cdot x=30\)

\(\Rightarrow x=10\)

`@` `\text {Ans}`

`\downarrow`

`5.x + 10.9 = 990`

`\Rightarrow 5x + 90 = 990`

`\Rightarrow 5x = 990 - 90`

`\Rightarrow 5x = 900`

`\Rightarrow x = 900 \div 5`

`\Rightarrow x = 180`

Vậy, `x = 180`

\(1045 \div [ 215 - (3 . x - 24 ) ] = 5\)

`\Rightarrow 1045 \div (215 - 3x + 24) = 5`

`\Rightarrow 191 + 3x = 1045 \div 5`

`\Rightarrow 191 + 3x = 209`

`\Rightarrow 3x = 209 - 191`

`\Rightarrow 3x =18`

`\Rightarrow x = 18 \div 3`

`\Rightarrow x = 6`

Vậy, `x = 6.`

5x+10.9=990

=>5x+90=990

=>5x=990-90

=>5x=900

=>x=900:5

=>x=180

______________

1045:[215-(3x-24)]=5

=>215-(3x-24)=1045:5

=>215-(3x-24)=209

=>3x-24=215-209

=>3x-24=6

=>3x=6+24

=>3x=30

=>x=30:3

=>x=10

de bai la gi vay

Bàn này hỏi gì vậy ? 

a, (17x-25):8=81-65

(17x-25):8=16

17x-25=16:8

17x-25=2

17x=2+25

17x=27

x=27:17

x=27/17

b,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

c,231-(x-6)=103

x-6=231-103

x-6=128

x=128+6

x=134

XEM LẠI GIÙM MÌNH BẠN NHA!

đề bài: (17x-25):8+65= 81

     (17x-25):8=81-65=16

      17x-25= 16 . 8= 128

     17x = 128+25=153

         x = 153:17=9

b, Đề bài 720:[41-(2x-5)]=8.5

              720:[41-(2x-5)]=40

            41-(2x-5)=720:40=18

                2x-5=41-18=23

               2x = 23+5=28

                 x = 28:2= 14

c, 231-(x-6)=1339:13=103

    x-6=231-103=128

     x= 128 + 6= 134

Đúng thì **** bạn

\(36\div\left[7.\left(x-3\right)+4\right]=6\)

\(\Rightarrow7.\left(x-3\right)+4=36\div6\)

\(\Rightarrow7.\left(x-3\right)+4=6\)

\(\Rightarrow7.\left(x-3\right)=6-4\)

\(\Rightarrow7.\left(x-3\right)=2\)

\(\Rightarrow x-3=2\div7\)

\(\Rightarrow x-3=\frac{2}{7}\)

\(\Rightarrow x=\frac{2}{7}+3\)

\(\Rightarrow x=\frac{23}{7}\)

\(36:\left[7.\left(x-3\right)+4\right]=6\)

\(7.\left(x-3\right)+4=36:6\)

\(7.\left(x-3\right)+4=6\)

\(7.\left(x-3\right)=6-4\)

\(7.\left(x-3\right)=2\)

\(x-3=2:7\)

\(x-3=\frac{2}{7}\)

\(x=\frac{2}{7}+3\)

\(x=\frac{23}{7}\)

\(\dfrac{1}{1\cdot2}+\dfrac{1}{2\cdot3}+\dfrac{1}{3\cdot4}+.......+\dfrac{1}{x\cdot\left(x+1\right)}=\dfrac{122}{123}\)

\(\Leftrightarrow1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+......+\dfrac{1}{x}-\dfrac{1}{x+1}=\dfrac{122}{123}\)

\(\Leftrightarrow1-\dfrac{1}{x+1}=\dfrac{122}{123}\)

\(\Leftrightarrow\dfrac{1}{x+1}=\dfrac{1}{123}\)

\(\Leftrightarrow x=122\)

\(445-52+155+452\\ =\left(445+155\right)+\left(452-52\right)\\ =600+4000\\ =1000\\ 102\cdot55-102\cdot73+51\cdot36\\ =102\cdot\left(55-73\right)+51\cdot36\\ =102\cdot\left(-18\right)+102\cdot18\\ =0\\ 4\cdot5\cdot2\cdot25\cdot5-1000\\ =5000-1000\\ =4000\\ 8782-291\cdot13\\ =4999\\ 254+\left\{38\cdot\left[\left(42-16\right):2\right]\right\}\\ =254+\left[38\cdot\left(26:2\right)\right]\\ =254+\left(38\cdot13\right)\\ =748\\ \left(2791\cdot34+7882:14\right)\cdot0+1510-510:2\\ =1510-255\\ =1255\)

a. \(445-52+155+452=\left(445+155\right)+\left(452-52\right)=600+400=1000\)

b. \(102\cdot55-102\cdot73+51\cdot36=102\left(55-73+18\right)=102\cdot0=0\)

c.\(4\cdot5\cdot2\cdot25\cdot5-1000=4\cdot25\cdot5\cdot5\cdot2-1000=100\cdot50-1000=5000-1000=4000\)

d. \(8782-291\cdot13=8782-3783=4999\)

e. \(254+\left\{38\left[\left(42-16\right)\div2\right]\right\}=254+\left\{30\cdot13\right\}=254+494=748\)

f. \(\left(2791\cdot34+7882\div14\right)\cdot0+1510-510\div2=0+1510-255=1255\)\

15,4 - ( 3 . x + 0,8 ) . 2 = 6

          ( 3 . x + 0,8 ) . 2 = 15,4 - 6

          ( 3 . x + 0,8 ) . 2 = 9,4

            3 . x + 0,8        = 9,4 : 2

            3 . x + 0,8        = 4,7

            3 . x                 = 4,7 - 0,8

            3 . x                 = 3,9

                 x                 = 3,9 : 3

                 x                 = 1,3

Vậy x = 1,3

15,4 - (3x + 0,8) . 2 = 6

( 3x + 0,8). 2 = 9,4

3x + 0,8 = 4,7

3x = 3,9

=> x = 1,3

15,4 - ( 3 . x +0,8 ) . 2 =6

(3x + 0,8) * 2 = 15,4 - 6

(3x + 0,8) * 2 = 9,4

3x +  0,8 = 9,4 :2

3x + 0,8 = 4,7

3x = 4,7 - 0,8 

3x = 3,9

x= 3,9 : 3

x= 1,3