电子课本网 第79页

第79页

信息发布者:
A
$\frac{1}{a-1}$
$\frac{2m-2}{m^2}$
$解:原式=\frac{2(x+3)}{3y}$
$ \begin{aligned} 解:原式&=\frac {(x^2+y^2)(x+y)(x-y)}{(x-y)^2}·\frac {y-x}{x^2+y^2} \\ &=-x-y \\ \end{aligned}$
$解:原式=\frac {xy-y^2-x^2-xy}{(x+y)(x-y)}×\frac {x+y}{x^2+y^2}=\frac {-(x^2+y^2)}{(x+y)(x-y)}×\frac {x+y}{x^2+y^2}=-\frac 1{x-y}$
$当x=2,y=-1时,原式=-\frac 13$
$解:原式=\frac {x+y}x$
$∵\sqrt{x-3}+y^2-4y+4=0$
$∴\sqrt{x-3}+(y-2)^2=0$
$根据非负数的性质可得,x=3,y=2$
$∴原式=\frac {3+2}3=\frac 53$