第88页 - 亮点给力提优课时作业本八年级数学江苏版

B

A

1

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

$=\frac {a}{a+1}-\frac {a-1}{a} · \frac {a(a+2)}{(a+1)(a-1)}$

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

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

$=\frac {a²-4-a-8}{(a+2)²} · \frac {a+2}{a-4}$

$= \frac {(a-4)(a+3)}{(a+2)²} · \frac {a+2}{a-4}$

$= \frac {a+3}{a+2}$

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

当$ x=-3$时，原式$=\frac {-3+2}{-3}=\frac {1}{3}$

A

B