第89页 - 经纶学典学霸八年级数学上下册【江苏国标】

A

C

ab

a+1

1

$解:原式=\frac{a^{2}}{(a-1)^{2}}×\frac{a-1}{a}-\frac{1}{a-1}$

$=\frac{a-1}{a-1}$

$=1$

$解:原式=\frac{3m+n}{m}×\frac{m}{(3m+n)(3m-n)}$

$=\frac{1}{3m-n}$

$解:原式=\frac {(x-y)^{2}}{x}×\frac {x}{(x+y)(x-y)}=\frac{x-y}{x+y}$

$解:原式=\frac {a^{2}-a+2a-2+a+3}{a+2}×\frac {a+2}{(a+1)(a-1)}$

$=\frac {(a+1)^{2}}{(a+1)(a-1)}$

$=\frac {a+1}{a-1}$

$解:原式= \frac {2x-1}{x-2}×\frac {(x+2)(x-2)}{x(2x-1)}=\frac {x+2}{x}$

$当x=-3时,原式=\frac {1}{3}$

$解:原式=\frac{a}{a-b}×\frac{(a-b)^{2}}{(a+b)(a-b)}-\frac{a-b}{a+b}$

$=\frac{a}{a+b}- \frac{a-b}{a+b}$

$=\frac{b}{a+b}$

$∵b-2a=0，∴b=2a$

$∴原式=\frac{2a}{a+2a}=\frac{2}{3}$

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