8. 通分：
(1) $\frac{1}{2a^3}$与$\frac{4}{3ab^2}$；
(2) $\frac{1}{4x-2x^2}$与$\frac{1}{x^2-4}$；
(3) $x-y$与$\frac{2y^2}{x+y}$；
(4) $\frac{1}{9-3x}$与$\frac{x-1}{x^2-9}$；
(5) $\frac{x}{6ab^2}$与$\frac{y}{9a^2bc}$；
(6) $\frac{1}{x^2-16}$与$\frac{1}{2x-8}$；
(7) $\frac{x}{ac}$与$\frac{y}{bc}$；
(8) $\frac{2x}{x^2-9}$与$\frac{x}{2x+6}$；
(9) $\frac{1}{x+1}$与$\frac{x}{x-1}$；
(10) $\frac{a}{2b}$，$\frac{1}{3a^2}$与$-\frac{5}{6abc}$；
(11) $\frac{b}{a^2-ab}$与$\frac{a}{a^2-b^2}$；
(12) $\frac{2}{x^2-6x+8}$，$\frac{1}{x^2+x-6}$与$\frac{3-x}{12+x-x^2}$。

(1) $\frac{3b^2}{6a^3b^2},\frac{8a^2}{6a^3b^2}$
(2) $-\frac{x+2}{2x(x+2)(x-2)},\frac{2x}{2x(x+2)(x-2)}$
(3) $\frac{x^2-y^2}{x+y},\frac{2y^2}{x+y}$
(4) $-\frac{x+3}{3x^2-27},\frac{3x-3}{3x^2-27}$
(5) $\frac{3acx}{18a^2b^2c},\frac{2by}{18a^2b^2c}$
(6) $\frac{2}{2x^2-32},\frac{x+4}{2x^2-32}$
(7) $\frac{bx}{abc},\frac{ay}{abc}$
(8) $\frac{4x}{2x^2-18},\frac{x^2-3x}{2x^2-18}$
(9) $\frac{x-1}{x^2-1},\frac{x^2+x}{x^2-1}$
(10) $\frac{3a^3c}{6a^2bc},\frac{2bc}{6a^2bc},-\frac{5a}{6a^2bc}$
(11) $\frac{ab+b^2}{a^3-ab^2},\frac{a^2}{a^3-ab^2}$
(12) [图1]