Đáp án:
`1)sqrt{x^2-2x+1}=3`
`<=>sqrt{(x-1)^2}=3`
`<=>|x-1|=3`
`<=>` \(\left[ \begin{array}{l}x-1=3\\x-1=-3\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}x=4\\x=-2\end{array} \right.\)
`2)9sqrt{x^2-6x+9}-81=0`
`<=>9sqrt{(x-3)^2}=81`
`<=>|x-3|=9`
`<=>` \(\left[ \begin{array}{l}x-3=9\\x-3=-9\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}x=12\\x=-6\end{array} \right.\)
`3)2sqrt{x-1}-3=15`
Điều kiện:`x-1>=0<=>x>=1`
`pt<=>2\sqrt{x-1}=18`
`<=>\sqrt{x-1}=9`
`<=>x-1=81`
`<=>x=82(tm)`
