Question

Tìm x, biết: 3^x+1 - 8 . 3^x = -405

 

Answer 1

`3^(x + 1) - 8 . 3^x = -405`

`=> 3^x  . 3 - 8 . 3^x = -405`

`=> 3^x . (3-8)=-405`

`=> 3^x . (-5)=-405`

`=> 3^x = (-405):(-5)`

`=> 3^x=81`

`=>3^x=3^4`

`=>x=4`

Vậy: `x=4`

Answer 2

\(3^{x+1}-8.3^x=-405\)
\(3^x.3-8.3^x=-405\)
\(3^x.\left(3-8\right)=-405\)
\(3^x.\left(-5\right)=-405\)
\(3^x=-405:\left(-5\right)\)
\(3^x=81\)
\(3^x=3^4\)
\(x=4\)