`@Sun` 

`log_2 (x^2 -2x -1) = 3`

`đk : x^2 -2x - 1 > 0` 

`<=> {(x > 1-sqrt2),(x> 1+sqrt2):}` 

`<=> x > 1 + sqrt2` 

`pt(1)` trở thành : 

`x^2 -2x - 1 = 2^3`

`<=> x^2 -2x - 1 = 8`

`<=> x^2 - 2x - 9 = 0`

`<=>` \(\left[ \begin{array}{l}x=1+\sqrt{10}(tm)\\x=1-\sqrt{10}(l)\end{array} \right.\)