第87页 - 经纶学典学霸八年级数学上下册【江苏国标】

A

C

A

-a

$\frac{y²}{4}$

$\frac {y-x}{y^{2} }$

(1+m)²

x≠3且x≠4且x≠-5

$-\frac{x-y}{x+y}$

$ \begin{aligned}解:原式&=\frac{(a-b)²}{b²}·\frac{b}{(a+b)(a-b)} \\ &=\frac{a-b}{ab+b²}. \\ \end{aligned}$

$ \begin{aligned}解:原式&=-\frac{x²}{y²}·\frac{y^{3} }{x^{3} }÷\frac {1}{x^{2} y^{2} } \\ &=-\frac {x^{2} }{y^{2} }·\frac {y^{3} }{x^{3} }·x^{2} y^{2}\ \\ &=-xy^{3} . \\ \end{aligned}$

$ \begin{aligned}解:原式&=\frac{x-1}{x}·\frac{x(x+1)}{(x-1)(x+1)} \\ &=1. \\ \end{aligned}$

$ \begin{aligned}解:原式&=\frac{a+3}{1-a}÷ \frac {a(a+3)}{(1-a)^{2} } \\ &=\frac{a+3}{1-a} ·\frac{(1-a)^{2} }{a(a+3)} \\ &= \frac{1-a}{a}. \\ \end{aligned}$