零五网 › 全部参考答案› 启东中学作业本 › 启东中学作业本八年级数学江苏版宿迁专版 › 第66页

第66页

信息发布者：

$-1$

$\frac{1}{x}$

$ \begin{aligned}解:原式&=\frac {6}{6a}+\frac {3}{6a}+\frac {2}{6a} \\ &=\frac{11}{6a} \\ \end{aligned}$

$ \begin{aligned} 解:原式&=\frac {y(x-y)}{(x+y)(x-y)}+\frac {2y^2}{(x+y)(x-y)} \\ &=\frac {xy+y^2}{(x+y)(x-y)} \\ &=\frac {y}{x-y} \\ \end{aligned}$

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

$ \begin{aligned} 解:原式&=\frac {m(m-n)}{m^2-n^2}-\frac {m(m+n)}{m^2-n^2}-\frac {m^2}{m^2-n^2} \\ &=\frac {-2mn-m^2}{m^2-n^2} \\ &=-\frac{m^2+2mn}{m^2-n^2} \\ \end{aligned}$

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

$\hspace{1.4cm}=\frac {x+1+x^2-3x}{(x+1)(x-1)}$

$\hspace{1.4cm}=\frac {x^2-2x+1}{(x+1)(x-1)}$

$\hspace{1.4cm}=\frac{(x-1)^2}{(x+1)(x-1)}$

$\hspace{1.4cm}=\frac{x-1}{x+1}.$

$把x=2代入，得原式=\frac{2-1}{2+1}=\frac{1}{3}.$