第11页 - 数学 - 电子课本网

$一\frac{1}{4m}$

$\frac {x^2y^4}{9m^2n^2}$

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

$\frac {ab^2}{2a^2b+ab}$

-3

3

4

$解：原式=\frac {y^2}{4a^2x^4}×\frac {-8x^3}{a^3y^3}$

$=-\frac {2}{a^5xy}$

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

$=\frac {y^2}{x+y}$

$解：原式=\frac {m-15}{m^2-9}+\frac {2(m+3)}{m^2-9}$

$=\frac {3m-9}{m^2-9}$

$=\frac{3}{m+3}$

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

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

$=1$

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

$=\frac{x+1}{x-2}\ $

$当x=0时，原式=一\frac{1}{2}\ $

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

$=\frac{2}{x一y}$

$将\begin{cases}{ x=2 }\ \\ {y=1\ } \end{cases}代入$

$得\frac {2}{x-y}=2$