Bài `4` `:`

`a)`

`3222-(x-235)=2357`

`x-235=3222-2357`

`x-235=865`

`x=865+235`

`x=1100`

Vậy `x=1100`

`b)`

`(x-28).10=350`

`x-28=350:10`

`x-28=35`

`x=35+28`

`x=63`

Vậy `x=63`

`c)`

`2^x` + `12` = `44`

`2^x`           = `44-12`

`2^x`           = `36`

mà `36` = `2^5`

hay `2^x` = `2^5`

`⇒` `x=5`

Vậy `x=5`

`d)`

`x^6` : `x^2` = `81`

`x^(6-2)`      = `81`

`x^4`            = `81`

mà `81` = `3^4`

hay `x^4` = `3^4`

`⇒` `x=3`

Vậy `x=3`

`e)`

`(3x+1)^2` - `2020^0` = `3` . `2^4`

`(3x+1)^2` - `1` = `48`

`(3x+1)^2`        = `48+1`

`(3x+1)^2`        = `49`

 mà `49` = `7^2`

hay `(3x+1)^2` = `7^2`

`⇒` `3x+1` = `7`

      `3x`     = `7-1`

      `3x`     = `6`

      `x`       = `3`

Vậy `x=3`

`f)`

`3^x` + `3^(x+3)` = `252`

`3^x` + `3^x` + `3^3` = `252`

`3^x` . `(1+27)` = `252`

`3^x` . `28` = `252`

`3^x` = `252÷28`

`3^x` = `9`

mà `9` = `3^2`

hay `3^x` = `3^2`

`⇒` `x=2`

Vậy `x=2`

bài 4:Tìm x∈N,biết:

a)3222-(x-235)=2357

x-235=3222-2357

x-235=865

x=865+235

x=1100

b)(x-28).10=350

x-28=350:10

x-28=35

x=35+28

x=63

c)`2^x`+12=44

`2^x`=44-12

`2^x`=32

`2^x`=`2^5`

vì `2^x`=`2^5`

⇒x=5

d)`x^6`:`x^2`=81

`x^6-2`=81

`x^4`=81

`x^4`=`3^4`

vì `x^4`=`3^4`

⇒x=3

e)(3x+1)²-`2020^0`=3.`2^4`

(3x+1)²-1=48

(3x+1)²=48+1

(3x+1)²=49

(3x+1)²=`7^2`

3x+1=`7^2-2`

3x+1=7

3x=7-1

3x=6

x=6:3

x=2

f)`3^x`+`3^x+3`=252

`3^x`+`3^x`.`3^3`=252

`3^x`.(1+27)=252

`3^x`.28=252

`3^x`=252:28

`3^x`=9

`3^x`=`3^2`

vì `3^x`=`3^2`

⇒x=2