bài 1
`a)`
`2sqrt54-2/5sqrt150-3sqrt24`
`=2.sqrt(9.6)-2/5sqrt(25.6)-3sqrt(4.6)`
`=2.3sqrt6-2/5 . 5sqrt6-3.2sqrt6`
`=6sqrt6-2sqrt6-6sqrt6`
`=-2sqrt6`
`b)`
`(sqrt99-sqrt18-sqrt11).sqrt11+3sqrt22`
`=(3sqrt11-3sqrt2-sqrt11).sqrt11+3sqrt22`
`=3.sqrt(11^2)-3.sqrt22-sqrt(11^2)+3sqrt22`
`=33-11`
`=22`
bài 2
`a)`
`sqrt(9x^2)=18`
`<=>3|x|=18`
`<=>|x|=6`
`<=>`\(\left[ \begin{array}{l}x=6\\x=-6\end{array} \right.\)
vậy `S={6;-6}`
`b)`
`sqrt(4x^2-12x+9)=7`
`<=>sqrt((2x-3)^2)=7`
`<=>|2x-3|=7`
`<=>` \(\left[ \begin{array}{l}2x-3=7\\2x-3=-7\end{array} \right.\) `<=>`\(\left[ \begin{array}{l}2x=10\\2x=-4\end{array} \right.\) `<=>`\(\left[ \begin{array}{l}x=5\\x=-2\end{array} \right.\)
vậy `S={5;-2}`
