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222-9+11+12:2*14+14 = ? ( )

Toán Lớp 6: Bài 2 a, 5-x=3 b, |x+1|-2020=1 c, x/7=x+15/42

Toán Lớp 6: Bài 2
a, 5-x=3
b, |x+1|-2020=1
c, x/7=x+15/42

Comments ( 2 )

  1. a,

    5-x=3

        x= 5 – 3

        x= 2 

    b.

    |x+1|-2020=1

    |x+1| = 2020 + 1

    |x+1| = 2021

    text{-> x + 1 = 2021 hoặc x + 1= -2021}

    Ta có :

    x + 1 = 2021

           x = 2021 – 1

           x = 2020

    Hoặc

    x + 1= -2021

          x = ( -2021 ) – 1 

          x = – 2022

    -> x ∈ { 2020 ; – 2022 }

    c.

    x/7=(x+15)/42

     7( x + 15 ) = 42x

    7x + 105 = 42x

    ( 42 – 7 )x = 105

    35x = 105

        x = 105 : 35

        x = 3

  2. a, 5 – x = 3

    ->x = 5 –  3

    ->x = 2

    __________________________________

    b, |x+1|-2020=1

    -> |x+1| =1 + 2020

    ->|x+1| = 2021

    ->  x + 1 = 2021   (h)     x + 1 = -2021

            x  = 2021 – 1           x = -2021 – 1

            x  = 2020                  x = -2022 

    vậy x ∈ {2020, -2022}

    ________________________________________

    c, x/7 =  $\dfrac{x+15}{42}$ 

    ->x . 42 = (x + 15) . 7

    ->x . 42 = 7x + 105

    ->(42 – 7) .x=105

    ->35 . x = 105

    -> x = 105 : 35 

    ->x = 3

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222-9+11+12:2*14+14 = ? ( )