2 x ( x - 31 ) + 100 = 210

2 x ( x - 31 ) = 210 - 100

2 x ( x - 31 ) = 110

x - 31 = 110 : 2 

x - 31 = 55

x = 55 + 31

x = 86

Sai thì bỏ qua -_-

x+(x+1)+(x+2)+...+(x+100) = 210

=> 101x + 100 x (100 + 1) :2 = 210

=> 101x + 5050 = 210

=> 101x = 210 - 5050

=> 101x = -4840

=> x = -4840 : 101

=> x = -4840/101

tính

x+(x+1)+(x+2)+...+(x+100)=210

(100x) + ( 1+2+...+100 ) = 210

 (100x)   + 5050 = 210

   100x    = 210 - 5050 = -4840

         x = -4840 : 100

            x = -48,4

ta co: x+120-210+111+x=100²

         2x+120-210+111=10000

        2x=10000-111+210-120

       2x=9979

      x=9979:2

      x=4989,5

đung rồi duyệt đi

a) (125 - x) + 25 = 98

125 - x = 98 - 25

125 - x = 73

x = 125 - 73

x = 52

b) 100 : (x + 20) = 68 : 34

100 : (x + 20) = 2

x + 20 = 100 : 2

x + 20 = 50

x = 50 - 20

x = 30

c) (3x + 12) . 5 = 25 . 4 - 10

(3x + 12) . 5 = 100 - 10

(3x + 12) . 5 = 90

3x + 12 = 90 : 5

3x + 12 = 18

3x = 18 - 12

3x = 6

x = 6 : 2

x = 3

d) 210 : (2x - 3) - 20 = 10

210 : (2x - 3) = 10 + 20

210 : (2x - 3) = 30

2x - 3 = 210 : 30

2x - 3 = 70

2x = 70 + 3

2x = 73

x = 73/2

a, ( 125 - x ) + 25 = 98

⇒ 125 - x = 73

⇒ x = 52.

Vậy..

b, 100 : ( x + 20 ) = 68 : 34

⇒ 100 : ( x + 20 ) = 2

⇒ x + 20 = 50

⇒ x = 30

Vậy...

c, ( 3 . x + 12 ) . 5 = 25 . 4 - 10

⇒ ( 3 . x + 12 ) . 5 = 90

⇒ 3 .x + 12 = 18

⇒ 3x = 6

⇒ x = 2.

Vậy...

d, 210 : ( 2 .x - 3 ) - 20 = 10

⇒ ( 2 .x - 3 ) - 20 = 21

⇒ 2x - 3 = 41

⇒ 2x = 44

⇒ x = 22.

Vậy..

Cho mk chỉnh lại câu cuối:

 d, 210 : ( 2 .x - 3 ) - 20 = 10

⇒ 210 : ( 2 .x - 3 ) = 30

⇒ 2 . x - 3 = 7

⇒ 2x = 10

⇒ x = 5.

Vậy..

\(580-\left(+200\right)-210-100=380-210-100\)

                                                               \(=170-100\)

                                                              \(=70\)

=580-(200)-210-100

=380-210-100

=170-100

=70

   \(580-(+200)-210-100\)

=\(380-210-100\)

=\(170-100\)

=\(70\)

k cho mình ngăn

500 – (–200 ) – 210 – 100;

= 500 + 200 – 210 – 100;

= 500 + 200 – (210 + 100)

= 700 – 310 = 390.