第67页 - 江苏版实验班提优训练数学八年级上下册答案

D

a≠3

$ \begin{aligned}解:原式&=\frac {(\frac {1}{3}x-\frac {1}{5}y)×30}{(2x+\frac {1}{6})×30} \\ &=\frac{10x-6y}{60x+5} \\ \end{aligned}$

$ \begin{aligned}解:原式&=\frac {(0.2x-\frac {1}{2}y)×60}{(\frac {1}{3}x+\frac {1}{4})×60} \\ &=\frac{12x-30y}{20x+15} \\ \end{aligned}$

B

$-\frac{a-2}{2a-2}$

$解:∵x²-3x+1=0，∴x≠0，$

$∴x+\frac{1}{x}=3.\ $

$∴x²+\frac{1}{x²}=(x+\frac{1}{x})²-2=9-2=7.$

$解:设\frac {y+z}{x}=\frac{x+z}{y}=\frac {x+y}{z}=k，\ $

$则y+z=kx，x+z=ky，x+y=kz，\ $

$∴2x+2y+2z=k(x+y+z).\ $

$∵x+y+z≠0，∴k=2.\ $

$∴原式=\frac{2z-z}{2z+z}=\frac{z}{3z}=\frac{1}{3}.$