8. 分式$\frac{a}{a^{2} - b^{2}}$，$\frac{b}{a^{2} + 2ab + b^{2}}$，$\frac{c}{a^{2} - 2ab + b^{2}}$的最简公分母是
$(a - b)^{2}(a + b)^{2}$
.
答案：8.$(a - b)^{2}(a + b)^{2}$
9. 已知最简分式$\frac{1}{2y^{a}}$与$-\frac{1}{bxy}$($a$，$b$是常数，且$b\neq0$)的最简公分母为$10xy^{3}$，则$a$的值为
3
，$b$的值为
5或10
.
答案：9.3 5或10
10. （教材变式）通分：
（1）$\frac{a + b}{(a + 2b)(a - 2b)}$，$\frac{a + b}{(2b + a)(2b - a)}$；
（2）$\frac{a}{a^{2} - 4a + 4}$，$\frac{b}{2a^{2} - 8a + 8}$，$\frac{c}{2a - 4}$；
（3）$\frac{2m}{9m + 15n}$，$\frac{3n}{6m - 10n}$，$\frac{2m + 5}{25n^{2} - 9m^{2}}$；
（4）$\frac{x}{x - y}$，$\frac{y}{x^{2} + 2xy + y^{2}}$，$\frac{2}{y^{2} - x^{2}}$.
答案：10.(1)$\frac {a + b}{(a + 2b)(a - 2b)}$,$-\frac {a + b}{(a + 2b)(a - 2b)}$ (2)$\frac {2a}{2(a - 2)^{2}}$,$\frac {b}{2(a - 2)^{2}}$,$\frac {c(a - 2)}{2(a - 2)^{2}}$ (3)$\frac {4m(3m - 5n)}{6(3m + 5n)(3m - 5n)}$,$\frac {9n(3m + 5n)}{6(3m + 5n)(3m - 5n)}$,$\frac {6(2m + 5)}{6(3m + 5n)(3m - 5n)}$
(4)$\frac {x(x + y)^{2}}{(x - y)(x + y)^{2}}$,$\frac {y(x - y)}{(x - y)(x + y)^{2}}$,$\frac {2(x + y)}{(x - y)(x + y)^{2}}$
11. 已知分式$\frac{1}{3x^{2} - 3}$，$\frac{2}{x - 1}$.若$a$是这两个分式的分母的公因式，$b$是这两个分式的最简公分母，且$\frac{b}{a} = - 6$，试求这两个分式的值.
答案：11.根据题意，得$a = x - 1$,$b = 3(x + 1)(x - 1)$.$\because\frac {b}{a} = - 6$,
$\therefore\frac {3(x + 1)(x - 1)}{x - 1} = - 6$，即$3(x + 1) = - 6$，解得$x = - 3$.
$\therefore\frac {1}{3x^{2} - 3} = \frac {1}{3×( - 3)^{2} - 3} = \frac {1}{24}$,$\frac {2}{x - 1} = \frac {2}{ - 3 - 1} = - \frac {1}{2}$
