Đáp án:
`1)`
`A=3\sqrt{8}-\sqrt{50}-\sqrt{(\sqrt{2}-1)^2}`
`=3.\sqrt{4.2}-\sqrt{25.2}-|\sqrt{2}-1|`
`=6\sqrt{2}-5\sqrt{2}-(\sqrt{2}-1)`
`=6\sqrt{2}-5\sqrt{2}-\sqrt{2}+1`
`=0+1=1`
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`2)`
`A=\sqrt{50}-3\sqrt{8}+\sqrt{(\sqrt{2}-1)^2}`
`=\sqrt{25.2}-3\sqrt{4.2}+|\sqrt{2}-1|`
`=5\sqrt{2}-6\sqrt{2}+\sqrt{2}-1`
`=0-1=-1`
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`3)`
`A=\sqrt{9-4\sqrt{5}}-\sqrt{5}`
`=\sqrt{5-4\sqrt{5}+4}-\sqrt{5}`
`=\sqrt{(\sqrt{5})^2-2.2\sqrt{5}+2^2}-\sqrt{5}`
`=\sqrt{(\sqrt{5}-2)^2}-\sqrt{5}`
`=|\sqrt{5}-2|-\sqrt{5}`
`=\sqrt{5}-2-\sqrt{5}`
`=-2`
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`4)`
`A=\sqrt{7-4\sqrt{3}}+\sqrt{12+6\sqrt{3}}`
`=\sqrt{4-4\sqrt{3}+3}+\sqrt{3+6\sqrt{3}+9}`
`=\sqrt{2^2-2.2\sqrt{3}+(\sqrt{3})^2}+\sqrt{(\sqrt{3})^2+2.3.\sqrt{3}+3^2}`
`=\sqrt{(2-\sqrt{3})^2}+\sqrt{(\sqrt{3}+3)^2`
`=|2-\sqrt{3}|+|\sqrt{3}+3|`
`=2-\sqrt{3}+\sqrt{3}+3`
`=5`
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