`3^x = 81`

`3^x = 3^4`

`=> x = 4`

ai giúp em câu này ik

`400 : { 5 . [ 360 - ( 290 + 2 . 5^2)]}`

`=400 : { 5 . [ 360 - ( 290 + 2 . 25)]}`

`=400 : { 5 . [ 360 - ( 290 + 50)]}`

`= 400 : { 5 . [ 360 - 340]}`

` = 400 : { 5 . 20}`

` = 400 : 100`

` = 4`

`400 : { 5 . [ 360 - ( 290 + 2 . 5^2)]}`

`=400 : { 5 . [ 360 - ( 290 + 2 . 25)]}`

`=400 : { 5 . [ 360 - ( 290 + 50)]}`

` = 400 : { 5 . 20}`

` = 400 : 100`

` = 4`

Vì `540 < 620=>540 < 620^10`

sai rồi !

`(x-y-z)-(5x-2y)-(-3x-y)`

`=x-y-z-5x+2y+3x+y`

`=-4x+2y-z`

dấu trừ trước dấu ngoặc

đáp số của bạn như sau không?

-x + 2y - z

23 + 3x = 5⁶ : 5³

23 + 3x = 5^6-3

23 + 3x = 5³

23 + 3x = 125

3x = 102

x= 34

Viết lại đề cho rõ ràng ra nha cậu!

x ( 3 - x ) = 0

x = 0 hoặc 3 - x = 0

                      x = 3 - 0

                      x = 3

Vậy x = 0; x = 3

( x + 2 ) . ( 4x - 8 ) = 0

x + 2 = 0

x       = 0 - 2

x       = -2

4x - 8 = 0

4x      = 8

x        = 2

Vậy x = -2; x = 2

21x - 17 - 15x = 25

21x - 15x - 17 = 25

6x            - 17 = 25

6x = 25 + 17

6x = 42

x = 7

123 - 5 ( x + 4 ) = 38

5 ( x + 4 ) = 123 - 38

5 ( x + 4 ) = 85

( x + 4 ) = 17

x = 13

1 - ( 3x-15) : 3 = 0

( 3x - 15 ) : 3 = 1 - 0

( 3x - 15 ) : 3 = 1

( 3x - 15 ) = 3

3x = 18

x= 6

23 + 17 ( x+1 ) = 108

17 ( x+1 ) = 85

( x + 1 ) = 5

x = 4

`x.(3-x) = 0`

`=>` \(\left[{}\begin{matrix}x=0\\3-x=0\end{matrix}\right.=>\left[{}\begin{matrix}x=0\\x=3\end{matrix}\right.\)

`(x +2).(4x-8) = 0`

`=>` \(\left[{}\begin{matrix}x+2=0\\4x-8=0\end{matrix}\right.=>\left[{}\begin{matrix}x=-2\\4x=8\end{matrix}\right.=>\left[{}\begin{matrix}x=-2\\x=2\end{matrix}\right.\)

`21x - 17 - 15x = 25`

`(21x-15x)-17=25`

`6x-17=25`

`6x = 42`

`x =42:6`

`x=7`

`123 - 5.(x+4)=38`

`5.(x+4) = 123-38`

`5.(x+4)  =85`

`x+4=85:5`

`x+4=17`

`x=17-4`

`x=13`

`1-(3x-15):3=0`

`3x-15:3=1`

`3x - 5 = 1`

`3x = 6`

`x=6:3`

`x=2`

`23+17.(x+1)  =108`

`17.(x+1) = 108 - 23`

`17.(x+1) =85`

`x+1=85:17`

`x+1=5`

`x=5-1`

`x=4`

\(6.\left(x-39\right)=18\\ \left(x-39\right)=18:6\\ \left(x-39\right)=3\\ x=3+39\\ x=42.\)

.

`7x-39=3`

`7x=3+39`

`7x=42`

`x=42:7`

`x=6`

\(7x=3+39\Leftrightarrow7x=42\Leftrightarrow x=6\)

Vậy x = 6

\(6\left(x-39\right)=18\)

x - 39 = 18 : 6

x - 39 = 3

x = 3 + 39

x = 42

`6.(x - 39) = 18`

`x - 39 = 18 : 6`

`x - 39 = 3`

`x = 39 + 3`

`x = 42`