電子課本網(wǎng) › 第146頁

第146頁

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$解：原式?=a+2\sqrt {a}-a?$

$? =2\sqrt {a}?$

$解：原式?=\sqrt {4{(a+1)}^2}?$

$? =2(a+1)?$

$解：原式?=xy(x-y)?$

$∵?x=2-\sqrt {3}，??y=2+\sqrt {3}?$

$∴?xy=1，??x-y=-2\sqrt {3}?$

$∴原式?=1×(-2\sqrt {3})=-2\sqrt {3}?$

$解：原式?={(a-1)}^2+(a-1)+2={(a-1+1)}^2+1=a^2+1?$

$∵?a=\sqrt {2}?$

$∴原式?={(\sqrt {2})}^2+1=3?$

$解：?25\sqrt {2}×16\sqrt {3}÷10\sqrt {15}=8\sqrt {10}(\mathrm {cm})?$

$答：乙的寬為?8\sqrt {10}\mathrm {cm}。?$

$解：?\frac 1 {\sqrt {n+1}+\sqrt {n}}=\sqrt {n+1}-\sqrt {n}?$

$解：原式?=(\sqrt {2}-1)+(\sqrt {3}-\sqrt {2})+···+(\sqrt {10}-\sqrt {9})?$

$? =\sqrt {10}-1?$

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