a)  x - 105 : 21 = 15

x - 5 = 15

=> x = 20

b)  ( x - 105 ) : 21 = 15

x - 105 = 315

=> x = 420

c)  315 + ( 125 - x ) = 435

125 - x = 120

=> x = 5

a)x - 105 : 21 = 15

    x - 5        =15

    x             =20

b) (x - 105) :21=15

     x -105         =315

     x                 =420

c) 315+ (125 - x ) =435

              125 - x   =-120            

                       x   =5

Bài 7:

a)(x-15)-75=0

⇔x-15=75

⇔x=90

b)575-(6x+70)=445

⇔6x+70=130

⇔6x=60

⇔x=10

c)x-105:21=15

⇔x-5=15

⇔x=20

d)(x-105):21=15

⇔x-105=315

⇔x=420

a) \(315+\left(125-x\right)=435\)

\(\Leftrightarrow125-x=435-315\)

\(\Leftrightarrow125-x=120\)

\(\Leftrightarrow x=125-120\)

\(\Leftrightarrow x=5\)

b) \(x:41=32\)

\(\Leftrightarrow x=32\cdot41\)

\(\Leftrightarrow x=1312\)

c) \(\left(x-105\right):21=15\)

\(\Leftrightarrow x-105=15\cdot21\)

\(\Leftrightarrow x-105=315\)

\(\Leftrightarrow x=315+105\)

\(\Leftrightarrow x=420\)

d) \(x-105:21=15\)

\(\Leftrightarrow x-5=15\)

\(\Leftrightarrow x=15+5\)

\(\Leftrightarrow x=20\)

a, 315 + ( 125 - x ) = 435 

              ( 125 - x) = 435 - 315 

               ( 125 - x ) = 320

                          x   = 320 - 125 

                          x = 195

bạn văn quang long tính sai rồi 435-315=120 chứ

1)\(x-105:21=15\)

\(x-5=15\)

\(x=15+5\)

\(x=20\)

Vậy \(x=20.\)

2)\(\left(x-105\right):21=15\)

\(\left(x-105\right)=15.21\)

\(x-105=315\)

\(x=315+105\)

\(x=420\)

Vậy \(x=412.\)

4)\(1818:\left(6x-37\right)=18\)

\(6x-37=1818:18\)

\(6x-37=101\)

\(6x=101+37\)

\(6x=138\)

\(x=138:6\)

\(x=23\)

Vậy \(x=23.\)

mk quên,còn phần 3) nữa:

3)\(\left(32+x\right):17=x\)

\(32+x=x.17\)

\(\Leftrightarrow x=2\)

Vậy \(x=2.\)

a ) 22 + 23 + x = 21 + | - 24 |

     45 + x         = 45

            x          = 0

b ) | - 3 | + | - 7 | = x + 3

      x + 3             = 3 + 7

      x + 3             = 10

            x             = 7

c ) | x | + 15 = - 9

     | x |         = -24

=> x rong

d ) x + 15 = 105 + ( -5 )

     x + 15 = 100

            x  = 85

e ) | x | + 45 = | - 17 | + | - 28 |

     | x | + 45 = 45

              | x | = 0

               x   = 0

x - 105 : 21 = 15

x - 105        = 315

x                =420

tk mk nhé

x-105:21=15

<=>x-5=15

<=>x=20

vậy x=20

x - 105 ÷ 21 = 15

x - 5 = 15

x      = 15 + 5

x      = 20