Đáp án+Giải thích các bước giải:
Bài `3:`
`b)\sqrt{4x-20}+3\sqrt{\frac{x-5}{9}}- 1/4\sqrt{16x-80}=6(x>=5)`
`<=>\sqrt{4(x-5)}+3.\sqrt{\frac{1}{9}}.\sqrt{x-5}-1/4.\sqrt{16(x-5)}=6`
`<=>2\sqrt{x-5}+3. 1/3 .\sqrt{x-5} -1/4 .4 .\sqrt{x-5}=6`
`<=>2\sqrt{x-5}+\sqrt{x-5}-\sqrt{x-5}=6`
`<=>2\sqrt{x-5}=6`
`<=>\sqrt{x-5}=6:2`
`<=>\sqrt{x-5}=3`
`<=>x-5=9`
`<=>x=14(tmđkxđ)`
`->S={14}`
Bài `4:`
`a)Đk:x\ne4`
`->x>=0`
`b)P=(\frac{\sqrt{x}}{x-4}+\frac{1}{\sqrt{x}+2}+\frac{2}{2-\sqrt{x}}):(\sqrt{x}+\frac{6-x}{\sqrt{x}+2}-2)(x\ne4,x>=0)`
`=(\frac{\sqrt{x}}{(\sqrt{x}+2)(\sqrt{x}-2)}+\frac{\sqrt{x}-2}{(\sqrt{x}-2)(\sqrt{x}+2)}-\frac{2(\sqrt{x}+2)}{(\sqrt{x}-2)(\sqrt{x}+2)}):(\frac{\sqrt{x}(\sqrt{x}+2)+6-x-2(\sqrt{x}+2)}{\sqrt{x}+2})`
`=(\frac{\sqrt{x}+\sqrt{x}-2-2\sqrt{x}-4}{(\sqrt{x}-2)(\sqrt{x}+2)}):(\frac{x+2\sqrt{x}+6-x-2\sqrt{x}-4}{\sqrt{x}+2})`
`=\frac{-6}{(\sqrt{x}-2)(\sqrt{x}+2)}.\frac{\sqrt{x}+2}{2}`
`=\frac{-3}{\sqrt{x}-2}`
