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______________.

$(a - b)^{2}(a + b)^{2}$

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________，$b$的值为________.

3 5或10

10. 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）$\frac{x}{x - y}$，$\frac{y}{x^{2}+2xy + y^{2}}$，$\frac{2}{y^{2}-x^{2}}$.

(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.

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 $x = -3$. $\therefore \frac{1}{3x^{2} - 3} = \frac{1}{3\times(-3)^{2} - 3} = \frac{1}{24}$, $\frac{2}{x - 1} = \frac{2}{-3 - 1} = -\frac{1}{2}$