Question

f,7^{x + 3} - 7^{x + 1} = 16464

tìm x

Answer 1

`7^x . 343 - 7^x . 7 = 16464`

`7^x . 336 = 16464`

`7^x = 49`

`x = 2`

Answer 2

7^{x + 3} - 7^{x + 1} = 16464

\(\Leftrightarrow7^x.7^3-7^x.7=16464\)

\(\Leftrightarrow7^x.\left(7^3-7\right)=16464\)

\(\Leftrightarrow7^x.336=16464\)

\(\Leftrightarrow7^x=49\Leftrightarrow7^x=7^2\)\(\Rightarrow x=2\)

Vậy x = 2