123,45 + 23,56 +76,44 + 54,55

= (123,45 + 54,55) + (23,56 + 76,44)

= 178 + 100

= 278

456 x 45 + 456 x 10 + - 456 x 55

=456 x (45 +10-55)

=456 x 0

=0

2,5 x 8,5 + 7,5 x 8,5 

=8,5 x (2,5 +7,5)

= 8,5 x 10

= 85

86 x 5 + 86 x 4 + 86

= 86 x (5+4+1)

= 86 x10

860

25 x 8 x 17 x 50

= 50 x 4 x 17 x 50

= 200 x 17 x 50 

= 200 x 50 x 17

= 10000 x 17

= 170000

(12 x 2 + 12 x 4 - 12 x 6 ) : ( 2 + 4 + 6 +... + 12 +14)

=(12 x (2 + 4 - 6) ) : ( 2 + 4 + 6 + ... + 12 + 14 )
= (12 x 0 ) : (2 + 4 + 6 + ... + 12 + 14 )

=0 : ( 2 + 4 + 6 + ... + 12 + 14)

= 0

a,\(\left(x-15\right):50+22=24\)

\(< =>\frac{\left(x-15\right)}{50}=2< =>x-15=100\)

\(< =>x=100+15=115\)

b,\(42-\left(2x+32\right)+12:2=6\)

\(< =>42-2x-32=0\)

\(< =>10-2x=0< =>x=\frac{10}{2}=5\)

Làm nốt :

c) \(134-2\left\{156-6\cdot\left[54-2\cdot\left(9+6\right)\right]\right\}\cdot x=86\)

=> 134 - 2{156 - 6 . [54 - 2 . 15]} . x = 86

=> 134 - 2{156 - 6 . [54 - 30]} . x = 86

=> 134 - 2{156 - 6. 24} . x = 86

=> 134 - 2{156 - 144} . x = 86

=> 134 - 2.12 . x = 86

=> 134 - 24 . x = 86

=> 24.x = 48

=> x = 2

Bài 2 : a) 120 : [21 - (4x - 4)] = 2³.3

=> 120 : [21 - (4x - 4)] = 8.3

=> 120 : [21 - (4x - 4)] = 24

=> 21 - (4x - 4) = 5

=> 4x - 4 = 16

=> 4x = 20

=> x = 5

b) 3.[205 - (x - 9)] - 486 = 0

=> 3.[205 - (x - 9)] = 486

=> 205 - (x - 9) = 162

=> x - 9 = 205 - 162 = 43

=> x = 43 + 9 = 52

c) 204 - 2{200 - 5.[64 - 2.(11 + 6)]} . x = 4

=> 204 - 2{200 - 5.[64 - 2.17]} . x = 4

=> 204 - 2{200 - 5 .[64 - 34]}.x = 4

=> 204 - 2{200 - 5.30} . x = 4

=> 204 - 2{200 - 150}.x = 4

=> 204 - 2.50 . x = 4

=> 2.50.x = 200

=> 100.x = 200

=> x = 2

Giải:

a) \(\dfrac{-5}{8}=\dfrac{x}{16}\) 

\(\Rightarrow x=\dfrac{16.-5}{8}=-10\) 

\(\dfrac{3x}{9}=\dfrac{2}{6}\) 

\(\Rightarrow3x=\dfrac{2.9}{6}=3\) 

\(\Rightarrow x=1\)

b) \(\dfrac{x+3}{15}=\dfrac{1}{3}\)  

\(\Rightarrow x+3=\dfrac{1.15}{3}=5\) 

\(\Rightarrow x=2\)

\(\dfrac{6}{2x+1}=\dfrac{2}{7}\) 

\(\Rightarrow2x+1=\dfrac{6.7}{2}=21\) 

\(\Rightarrow x=10\)

c) \(\dfrac{4}{x-6}=\dfrac{y}{24}=\dfrac{-12}{18}\) 

\(\Rightarrow\dfrac{4}{x-6}=\dfrac{-12}{18}\) 

\(\Rightarrow x-6=\dfrac{18.4}{-12}=-6\) 

\(\Rightarrow x=0\) 

\(\Rightarrow\dfrac{y}{24}=\dfrac{-12}{18}\) 

\(\Rightarrow y=\dfrac{-12.24}{18}=-16\) 

 \(\dfrac{3-x}{-12}=\dfrac{16}{y+1}=\dfrac{192}{-72}\) 

\(\Rightarrow\dfrac{3-x}{-12}=\dfrac{192}{-72}\) 

\(\Rightarrow3-x=\dfrac{192.-12}{-72}=32\) 

\(\Rightarrow x=-29\) 

\(\Rightarrow\dfrac{16}{y+1}=\dfrac{192}{-72}\) 

\(\Rightarrow y+1=\dfrac{16.-72}{192}=-6\) 

d) \(\dfrac{-2}{3}< \dfrac{x}{5}< \dfrac{-1}{6}\) 

\(\Rightarrow\dfrac{-20}{30}< \dfrac{6x}{30}< \dfrac{-5}{30}\) 

\(\Rightarrow6x\in\left\{-18;-12;-6\right\}\) 

\(\Rightarrow x\in\left\{-3;-2;-1\right\}\) 

\(\dfrac{-1}{5}\le\dfrac{x}{8}\le\dfrac{1}{4}\) 

\(\Rightarrow\dfrac{-8}{40}\le\dfrac{5x}{40}\le\dfrac{10}{40}\) 

\(\Rightarrow5x\in\left\{-5;0;5;10\right\}\) 

\(\Rightarrow x\in\left\{-1;0;1;2\right\}\) 

e) \(\dfrac{x+46}{20}=x\dfrac{2}{5}\) 

\(\Rightarrow\dfrac{x+46}{20}=x+\dfrac{2}{5}\) 

\(\Rightarrow\dfrac{x+46}{20}=\dfrac{5x+2}{5}\) 

\(\Rightarrow5.\left(x+46\right)=20.\left(5x+2\right)\) 

\(\Rightarrow5x+230=100x+40\) 

\(\Rightarrow5x-100x=40-230\) 

\(\Rightarrow-95x=-190\) 

\(\Rightarrow x=-190:-95\) 

\(\Rightarrow x=2\) 

\(y\dfrac{5}{y}=\dfrac{86}{y}\) 

\(\Rightarrow y+\dfrac{5}{y}=\dfrac{86}{y}\) 

\(\Rightarrow\dfrac{y^2+5}{y}=\dfrac{86}{y}\) 

\(\Rightarrow y^2+5=86\) 

\(\Rightarrow y^2=86-5\) 

\(\Rightarrow y^2=81\) 

\(\Rightarrow\left[{}\begin{matrix}y=9\\y=-9\end{matrix}\right.\) 

Chúc bạn học tốt!

1. [|x| + 3 ] . 15 - 5 = 70

2. 86 : { 2. [ 2x - 1 ]² - 7 } + 4² = 2. 3²

3. 20 - { 4² + [ x - 6 }] = 90

4. 24- |x + 8| = 3. [2⁵ - 5²  ]

5. 1000 : [ 30 + { 2^x - 6 }] = 3² + 4²

6. [ x + 1 ] chia hết [ x + 2 ] và x thuộc N

Baì làm

1) . [|x| + 3 ] . 15 - 5 = 70

      .[|x| + 3 ] . 15      = 70 + 5 

       [|x| + 3 ] . 15      = 75

      .[|x| + 3 ]             = 75 : 15

      .[|x| + 3 ]             = 5

        |x|                     = 5 - 3

       |x|                      = 2

=> \(\orbr{\begin{cases}x=2\\x=-2\end{cases}}\)

2). 86 : { 2. [ 2x - 1 ]² - 7 } + 4² = 2. 3²

     86 : { 2. [ 2x - 1 ]² - 7 } + 4² = 2. 9

     86 : { 2. [ 2x - 1 ]² - 7 } + 4² = 18

    86 : { 2. [ 2x - 1 ]² - 7 }          = 18 - 16

    86 : { 2. [ 2x - 1 ]² - 7 }          = 2

            { 2. [ 2x - 1 ]² - 7 }         = 86 : 2

          { 2. [ 2x - 1 ]² - 7 }           = 43

          2. [ 2x - 1 ]²                        = 43 + 7

         2. [ 2x - 1 ]²                         =  50

           . [ 2x - 1 ]²                     = 50 : 2

             [ 2x - 1 ]²                        = 25

           . [ 2x - 1 ]²                     = 5²

             2x -1                           = 5

             2x                               = 5+1

            2x                                = 6

             x                                 = 6: 2

             x                                 = 3

3) 20 - { 4² + [ x - 6 }] = 90

 20 - { 4² + [ x - 6 }]    = 90: 3

 20 - { 4² + [ x - 6 }]    = 30

        { 4² + [ x - 6 }]    = 30 + 20

        { 4² + [ x - 6 }]    = 50

         { 16 + [ x - 6 }]  = 50

                  [ x - 6 ]    = 50 -16

                  [ x - 6 ]    =  34

                   x            = 34 + 6 

                   x            =40

4) 24- |x + 8| = 3. [2⁵ - 5²  ]

4. 24- |x + 8| = 3.(32-25)

4. 24- |x + 8| = 3. 7

4. 24- |x + 8| = 21

4. 24- |x + 8| = 21

96-|x + 8| = 21

     |x + 8| = 96 - 21

     |x + 8| = 75

=> \(\orbr{\begin{cases}x+8=75\\x+8=-75\end{cases}}=>\orbr{\begin{cases}x=75-8\\x=-75-8\end{cases}}=>\orbr{\begin{cases}x=67\\x=-83\end{cases}}\)

5) 1000 : [ 30 + { 2^x - 6 }] = 3² + 4²

    1000 : [ 30 + { 2^x - 6 }] = 9 + 16 

    1000 : [ 30 + { 2^x - 6 }] = 25

               [ 30 + { 2^x - 6 }] = 1000 : 25

               [ 30 + { 2^x - 6 }] = 40

                         { 2^x - 6 }  = 40 + 30

                         { 2^x - 6 }  = 70

                         2^x            = 70 - 6

                         2^x            = 64

                         2^x            = 2⁶

                          x             = 6

6. [ x + 1 ] chia hết [ x + 2 ] và x thuộc N

    Ta có : x + 1 = x + 2 - 1

     Vì x + 1 \(⋮\)x + 2

=>  x + 2 - 1\(⋮\) x + 2

vì  x + 2 -1\(⋮\) x + 2 =>  1 \(⋮\)x+2

=> x + 2 \(\in\)Ư(1)

=>\(x+2=1=>x=1-2=>x=-1\)

=> mà x \(\in\)N lại có x = -1

=> x \(\in\) \(\varnothing\)

a) (25x32) : 8           

= 25 x (4 x 8) : 8

= (25 x 4) x (8:8)

= 100 x 1

=100

b, 24 x 11 + 6 x 86 x 4 + 72

= 24 x 11 + (6 x 4) x 86 + 24 x 3

= 24 x 11 + 24 x 86 + 24 x 3

= 24 x (11+86+3)

= 24 x 100

= 2 400

\(\left(25\times32\right):8=25\times32:8=25\times\left(32:8\right)=25\times4=100\\ 24\times11+6\times86\times4+72\\ =24\times11+24\times86+24\times3\\ =24\times\left(11+86+3\right)\\ =24\times100=2400\\ 36\times5+9\times79\times4+72\times8\\ =36\times5+36\times79+36\times16\\ =36\times\left(5+79+16\right)\\ =36\times100=3600\\ \left(56\times125\right):7=56\times125:7=\left(56:7\right)\times125=8\times125=1000\)

\(5.\left[225-\left(x-10\right)-125\right]=0\)

\(225-\left(x-10\right)-125=0:5\)

\(225-\left(x-10\right)-125=0\)

\(\left(x-10\right)-125=225-0\)

\(\left(x-10\right)-125=225\)

\(x-10=225+125\)

\(x-10=350\)

Mấy bài này làm theo thứ tứ trái sang phải, nhân chia trc cộng trừ sau thoi mà :>>>?

Quên, thứ tự ngoặc là { [ ( ) ] } nha :))))))))))))))))

A = 78 x 31 + 78 x 24 + 78 x 17 + 22 x 72

A = 78 x ( 31 + 24 + 17 ) + 22 x 72

A = 78 x 72 + 22 x 72

A = 72 x ( 78 + 22 ) 

A = 72 x 100

A = 7200

C = 53 x 39 + 47 x 39 - 53 x 21 - 47 x 21

C = 39 x ( 53 + 47 ) - 21 x ( 53 - 47 )

C = 39 x 100 - 21 x 6

C = 3900 - 126

C = 3774

ko pc tui thua bn 1 lp 

A = 78 x 31 + 78 x 24 + 78 x 17 + 22 x 72

A = 78 x ( 31 + 24 +17 ) + 22 x 72

A = 78 x 72 + 22 x 72

A = 72 x ( 78 + 22 )

A = 72 x 100

A = 7200