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電子課本網(wǎng) 第58頁

第58頁

信息發(fā)布者:
解:$(10x)^3 = -512,$$10x = -8,$$x = -0.8$
解:$(2x + 1)^3 = -1,$$2x + 1 = -1,$$2x = -2,$$x = -1$
解:設(shè)正方形邊長為$a,$則$a^2 = 10,$圓半徑$r = \frac{a}{2},$圓面積$S=\pi r^2=\pi(\frac{a}{2})^2=\frac{\pi a^2}{4}=\frac{10\pi}{4}\approx7.85\mathrm{cm}^2$
解:∵?$1<\sqrt 2<2$?
∴?$3 + \sqrt 2$?的整數(shù)部分?$a = 4,$?小數(shù)部分?$b = 3 + \sqrt 2-4=\sqrt 2-1$?
?$3 - \sqrt 2$?的整數(shù)部分?$c = 1,$?小數(shù)部分?$d = 3 - \sqrt 2-1 = 2 - \sqrt 2$?
∴?$\frac {a - c}{b + d}=\frac {4 - 1}{\sqrt 2-1 + 2 - \sqrt 2}=\frac 31=3$?