Đáp án+Giải thích các bước giải:
`a)\sqrt{x^2-16}-3\sqrt{x-4}=0(x>=4)`
`<=>\sqrt{(x-4)(x+4)}-3\sqrt{x-4}=0`
`<=>\sqrt{x-4}(\sqrt{x+4}-3)=0`
`<=>[(\sqrt{x-4}=0),(\sqrt{x+4}=3):}`
`<=>[(x-4=0),(x+4=9):}`
`<=>[(x=4(tm)),(x=5(tm)):}`
Vậy `S={4;5}`
`b)\sqrt{x+3+4\sqrt{x-1}}=3(x>=1)`
`<=>\sqrt{x-1+4\sqrt{x-1}+4}=3`
`<=>\sqrt{(\sqrt{x-1}+2)^2}=3`
`<=>|\sqrt{x-1}+2|=3`
`<=>\sqrt{x-1}+2=3(\sqrt{x-1}+2>=2)`
`<=>\sqrt{x-1}=1`
`<=>x-1=1`
`<=>x=2(tm)`
Vậy `S={2}`
