tìm x bt a.450:(x+5)=50 b.2^2021(x-2)=2^2022 c.106-(3x+5)=71 d.5^2x-3-2.5^2=5^2.3 e.x:15;x:20;x:24 và 200<x<300

`a, 450 : (x + 5) = 50`

  `x + 5 = 450 : 50`

  `x + 5 = 9`

  `x = 4`

Vậy `x = 4`

`b, 2^2021 · (x - 2) = 2^2022`

  `x - 2 = 2^2022 : 2^2021`

  `x - 2 = 2`

  `x = 4`

Vậy `x = 4`

`c, 106 - (3x + 5) = 71`

  `3x + 5 = 106 - 71`

  `3x + 5 = 35`

  `3x = 30`

  `x = 30 : 3`

  `x = 10`

Vậy `x = 10`

`d, 5^2x - 3 - 2 · 5^2 = 5^2 · 3`

  `25x - 3 - 2 · 25 = 25 · 3`

  `25x - 3 - 50 = 75`

  `25x = 75 + 50 + 3`

  `25x = 128`

  `x = 128 : 25`

  `x = 128/25`

Vậy `x = 128/25`

`e, x vdots 15, x vdots 20, x vdots 24` và `200 < x < 300`

Ta có:

`x vdots 15, x vdots 20, x vdots 24`

`=> x ∈ BC(15, 20, 24)`

Ta có:

`15 = 3 · 5`

`20 = 2^2 · 5`

`24 = 2^3 · 3`

`=>` $BCNN(15, 20, 24)$ `= 2^3 · 3 · 5 = 120`

`=> BC(15, 20, 24) = B(120) = {0; 120; 240; 360;...}`

Mà `200 < x < 300`

`=> x = 240`

Vậy `x = 240`