Tìm `x`, biết: (hình ảnh)

`Bạn tham khảo nhé :`

`a,` $3^{x-1}$ `-3=78`

$3^{x-1}$ `=78+3`

$3^{x-1}$ `=81`

$3^{x-1}$ `=` $3^{4}$

`⇒x-1=4`

`x=4+1`

`x=5`

`Vậy x=5`

`b,` $4^{x-1}$ `+3=67`

$4^{x-1}$ `=67-3`

$4^{x-1}$ `=64`

$4^{x-1}$ `=` $4^{3}$

`⇒x-1=3`

`x=3+1`

`x=4`

`Vậy x=4`

`c,` $3^{x-4}$ `-63=18`

$3^{x-4}$ `=18+63`

$3^{x-4}$ `=81`

$3^{x-4}$ `=` $3^{4}$

`⇒x-4=4`

`x=4+4`

`x=8`

`Vậy x=8`

`d,` $4^{x-3}$ `+15=79`

$4^{x-3}$ `=79-15`

$4^{x-3}$ `=64`

$4^{x-3}$ `=` $4^{3}$

`⇒x-3=3`

`x=3+3`

`x=6`

`Vậy x=6`

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