Bài 2: 

a: =>x-35=-23

=>x=12

b: =>|x-8|=13

=>x-8=13 hoặc x-8=-13

=>x=21 hoặc x=-5

Bài 1: 

a: =42-98-42+12-12=-98

b: =10x4x3x(-25)=40x(-25)x3=-1000x3=-3000

a, 2 x 31 x 12 + 4 x 6 x 42 + 8 x 27 x 3

= 2 x 12 x 31 + 4 x 6 x 42 + 8 x 3 x 27

= 24 x 31 + 24 x 42 + 24 x 27

= 24 x ( 31 + 24 + 27 )

= 24 x 82 

= 1968

b, 2 x 53 x 12 + 4 x 6 x 87 - 3 x 8 x 40

= 24 x 53 + 24 x 87 - 24 x 40

= 24 x ( 53 + 87 - 40 )

= 24 x 100

= 2400

c, Tương tự

a) = 1968

b) = 2400

đó là kq câu a) ; b)

**** Nha bn

a) \(\left(x+13\right):5=12\)

\(\Rightarrow x+13=12\cdot5\)

\(\Rightarrow x+13=60\)

\(\Rightarrow x=60-13\)

\(\Rightarrow x=47\)

b) \(23\cdot\left(42-x\right)=23\)

\(\Rightarrow42-x=23:23\)

\(\Rightarrow42-x=1\)

\(\Rightarrow x=42-1\)

\(\Rightarrow x=41\)

a: =>x-15=20

hay x=35

c: =>12x=360

hay x=30

a)Ta có:

\(\left\{{}\begin{matrix}\left|x+3\right|\ge0\\\left|x+9\right|\ge0\\\left|x+5\right|\ge0\end{matrix}\right.\)

\(\Rightarrow\left|x+3\right|+\left|x+9\right|+\left|x+5\right|\ge0\)

\(\Rightarrow4x\ge0\Rightarrow x\ge0\)

\(\Rightarrow\left|x+3\right|+\left|x+9\right|+\left|x+5\right|=x+3+x+9+x+5=3x+17=4x\)

\(\Rightarrow17=4x-3x\Rightarrow x=17\)

b)Tương tự câu a, ta chứng minh được \(x\ge0\)

\(\Rightarrow\left|x+1\right|+\left|x+2\right|+...+\left|x+98\right|+\left|x+99\right|=x+1+x+2+...+x+98+x+99=99x+4950=100x\)

\(\Rightarrow4950=100x-99x\Rightarrow x=4950\)

c)Ta có:

\(\left|x-1\right|+\left|x-5\right|=\left|x-1\right|+\left|5-x\right|=4=\left|x-1+5-x\right|\)

\(\Rightarrow1\le x\le5\Rightarrow x\in\left\{1;2;3;4;5\right\}\)

có cái nịt

giúp tôi nhá

a) 5(x+7) - 10 = 2^3 . 5

 5(x+7 ) -10 = 8 . 5 = 40

5(x+7) = 40 + 10 = 50

x + 7 = 50 : 5 = 10

x = 10 - 7 = 3

\(25-\left(25-x\right)=12+\left(42-65\right).\)

\(\Leftrightarrow25-25+x=12-23.\)

\(\Leftrightarrow x=-11.\)

Vậy \(x=-11.\)

25 - ( 25 - x ) = 12 + ( 42 - 65 )

25 - ( 25 - x ) = 12 + (-23)

25 - ( 25 - x ) = -11

25 - x = 25 - (-11)

25 - x = 36

x = 25 - 36

x = -11

25 - (25 - x) = 12 + (42 - 65)

25 - 25 + x = 12 + (-23)

x = - 11

\(25-\left(25-x\right)=12+\left(42-65\right).\)

\(\Leftrightarrow25-25+x=12-23.\)

\(\Leftrightarrow x=-11.\)

Vậy \(x=-11.\)

a,45 + x = 2x                                      e, 4x + 3x = 70

\(\Rightarrow2x-x=45\)                          \(\Rightarrow7x=70\)

\(\Rightarrow x=45\)                                   \(\Rightarrow x=10\)

Vậy x = 45                                          Vậy x = 10

b, 2 + x - 4 = 12                                  f, 6x - 18 = 0

\(\Rightarrow2+x=12+4\)                \(\Rightarrow6x=18\)

\(\Rightarrow2+x=16\)                         \(\Rightarrow x=3\)

\(\Rightarrow x=14\)                                  Vậy x = 3

Vậy x = 14                                         g, 72x : 36 = 2

c, 10 + x = 5 + 2x                              \(\Rightarrow72x=72\)

\(\Rightarrow2x+x=10+5\)             \(\Rightarrow x=1\)

\(\Rightarrow3x=15\)                                Vậy x = 1

\(\Rightarrow x=5\)                                     h, 13 + x = 5 + 2x

Vậy x = 5                                           \(\Rightarrow2x+x=13+5\)

d, 42 - 2x = 12                                    \(\Rightarrow3x=18\)

\(\Rightarrow2x=42-12\)                    \(\Rightarrow x=6\)

\(\Rightarrow2x=30\)                                Vậy x = 6

\(\Rightarrow x=15\)

Vậy x = 15

45 + x = 2x

x =45

2 + x - 4 =12

x - 2 = 12

x = 14

10 +x = 5 + 2x

-x = -5

x = 5

42 - 2x = 12

-2x = -30

x = 15

4x + 3x = 70

7x = 70

x = 10

6x - 18 = 0

6x = 18

x = 3

72x : 36 = 2

72x = 72

x = 1

13 +x = 5 +2x

-x = -8

x = 8

học tốt