a,
`(2x-1)^2=9`
`<=>`\(\left[ \begin{array}{l}2x-1=3\\2x-1=-3\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}2x=4\\2x=-2\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=2\\x=-1\end{array} \right.\)
b,
Ta có:
`5n+11\vdotsn+2`
`<=>5n+10+1\vdotsn+2` (vì `5n+10=5(n+2)\vdotsn+2`)
`<=>1\vdotsn+2`
`=>n+2∈Ư(1)`
`=>n+2∈{-1; 1}`
`=>n∈{-3; -1}`