Đáp án: $17:A$
$18:B$
$19:C$
$20:D$
$21:B$
$22:C$
$23:B$
Giải thích các bước giải:
Câu 17: $\sqrt{(3-\sqrt{2})^2}=|3-\sqrt{2}|=3-\sqrt{2}$
Câu 18:
`2b^2\sqrt{\frac{a^4}{4b^2}}(b>0)`
`=2b^2.|\frac{a^2}{2b}|`
`=2b^2.\frac{a^2}{2b}`
$=a^2b$
Câu 19:
$\sqrt{5+\sqrt{x}}=4(x≥0)$
$⇔5+\sqrt{x}=16$
$⇔\sqrt{x}=11$
$⇔x=121$ (thỏa mãn)
Câu 20:
$\sqrt{2x+1}=3(x≥-0,5)$
$⇔2x+1=9$
$⇔2x=8⇔x=4$ (thỏa mãn)
Câu 21:
`\sqrt{\frac{a}{b}}+\frac{a}{b}.\sqrt{\frac{b}{a}}(a;b>0)`
`=\sqrt{\frac{a}{b}}+\sqrt{\frac{b}{a}.\frac{a^2}{b^2}}`
`=\sqrt{\frac{a}{b}}+\sqrt{\frac{a}{b}}`
`=2.\sqrt{\frac{a}{b}}`
`=\frac{2\sqrt{a}}{\sqrt{b}}`
`=\frac{2\sqrt{ab}}{b}`
Câu 22:
`\frac{-8}{2\sqrt{2}}`
`=\frac{-(\sqrt{8})^2}{\sqrt{8}}`
`=-\sqrt{8}=-2\sqrt{2}`
Câu 23: $\sqrt{\sqrt{3}-\sqrt{2}}$=|\sqrt{3}-\sqrt{2}|=\sqrt{3}-\sqrt{2}$
