`#Rùa`
Đáp án+Giải thích các bước giải:
Bài 3:
`a)\sqrt{63y^3}/\sqrt{7y}` (`y >0`)
`=\sqrt{9y^2 .7y}/\sqrt{7y}`
`=(\sqrt{9y^2}.\sqrt{7y})/\sqrt{7y}`
`=|3y|`
`=3y`
`b)\sqrt{48x^3}/\sqrt{3x^6}` (`x>0`)
`=\sqrt{16. 3x^3}/\sqrt{x^3.3x^3}`
`=(\sqrt{16}.\sqrt{3x^3})/(\sqrt{x^3}.\sqrt{3x^3})`
`=4/\sqrt{x^3}`
`c)\sqrt{45ab^2}/\sqrt{20a}`
`=\sqrt{9b^2 . 5a}/\sqrt{4.5a}`
`=(\sqrt{9b^2}.\sqrt{5a})/(\sqrt{4}.\sqrt{5a})`
`=|3b|/4`
`d)\sqrt{16a^4 b^6}/\sqrt{128a^6 b^4}` (`a<0;b\ne0`)
`=\sqrt{16a^4 b^4 .b^2}/\sqrt{16a^4 b^4 .8a^2}`
`=(\sqrt{16a^4 b^4}.\sqrt{b^2})/(\sqrt{16a^4 b^4}.\sqrt{8a^2})`
`=|b|/\sqrt{8a^2}`
`=|b|/(|2a|.\sqrt{2})`
`=-|b|/(2a\sqrt{2})`
Bài 4:
`a)\sqrt{9(x+1)}=21` (`x ≥ -1`)
`<=> 3.\sqrt{x+1}=21`
`<=> \sqrt{x+1}=7`
`<=> x+1=49`
`<=> x=48` (TM)
Vậy `S={48}`
`b)\sqrt{3x}=\sqrt{12}` (`x ≥0`)
`<=> 3x=12`
`<=> x=4` (TM)
Vậy `S={4}`
`c) \sqrt{16(x-3)}=8` (`x ≥3`)
`<=> 4\sqrt{x-3}=8`
`<=> \sqrt{x-3}=2`
`<=> x-3=4`
`<=> x=7` (TM)
Vậy `S={7}`
`d)\sqrt{2x-3}=7` (`x ≥ 3/2`)
`<=> 2x-3=49`
`<=> 2x=52`
`<=> x=26` (TM)
Vậy `S={26}`
