1 câu trả lời
a) `\sqrt{32+12\sqrt{7}}`
`=\sqrt{2}.\sqrt{16+6\sqrt{7}}`
`=\sqrt{2}.\sqrt{9+2.3.\sqrt{7}+7}`
`=\sqrt{2}.\sqrt{(3+\sqrt{7})^2}`
`=\sqrt{2}.|3+\sqrt{7}|`
`=\sqrt{2}.(3+\sqrt{7})`
`=3\sqrt{2}+\sqrt{14}`
b) `\sqrt{18-6\sqrt{5})`
`=\sqrt{3}.\sqrt{6-2\sqrt{5}}`
`=\sqrt{3}.\sqrt{5-2\sqrt{5}+1}`
`=\sqrt{3}.\sqrt{(\sqrt{5}-1)^2}`
`=\sqrt{3}.|\sqrt{5}-1|`
`=\sqrt{3}.(\sqrt{5}-1)`
`=\sqrt{15}-\sqrt{3}`