$解:\ \ \ \ \ \ x^{2}=\frac {49}{16}$ $\ \ \ \ \ \ x=±\frac {7}{4}$
解:由题,ab=1,c+d=0 ∴原式=-1+0+1=0
$ 解:1\lt \sqrt {3}\lt 2$ $∴a=4,b=\sqrt {3}-1,∴a-b=5-\sqrt {3}$ $或a=5,b=\sqrt {3}-2,∴a-b=7-\sqrt {3}$
$\sqrt[{3}] {512},3.1415926,-0.456,0,\frac {5}{11},\sqrt {(-7)^{2}}$
$π,3.030030003···,-\sqrt[{3}] {9},\sqrt {0.1}$
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