Question

\(\dfrac{1}{5^{x-1_{ }}}\)+3x \(5^{2-x}\)= \(\dfrac{16}{125}\)

Answer 1

\(\dfrac{1}{5^{x-1}}+3\cdot5^{2-x}=\dfrac{16}{125}\)

=>\(\dfrac{1}{5^x\cdot\dfrac{1}{5}}+3\cdot\dfrac{25}{5^x}=\dfrac{16}{125}\)

=>\(\dfrac{80}{5^x}=\dfrac{16}{125}\)

=>\(5^x=125\cdot\dfrac{80}{16}=625=5^4\)

=>x=4

Answer 2

`1/(5^(x-1)) + 3 . 5^(2-x) = 16/125`

`=> 1/(5^x . 1/5 ) +3. 25/5^(x) = 16/125`

`=> 80/(5^x) = 16/125`

`=> 5^x = 16/125 . 80`

`=> 5^x =625`

`=> 5^x = 5^4`

`=> x = 4`

Vậy: `x=4`