`y10000`
$\text{Bài 1 :}$
`a )`
$\sqrt{75 . 48 }$
`= \sqrt{75} . \sqrt{48}`
`= 5\sqrt{3} . 4\sqrt{3}`
`= 60`
`b )`
`\frac{\sqrt{45ab²}}{\sqrt{20a}}`
`= \sqrt\frac{45ab²}{20a}`
`= \sqrt\frac{9b²}{4}`
`= \frac{\sqrt{9b²}}{\sqrt{4}}`
`= \frac{3b}{2}`
$\text{( a , b không âm )}$