1. 约分:
(1)$\frac {6ab^{2}}{3a^{2}b}$; (2)$\frac {6a^{4}c^{2}}{9a^{2}b^{2}}$;
(3)$\frac {2a - 2}{a^{2}-1}$; (4)$\frac {ma + mb - mc}{a + b - c}$;
(5)$\frac {a^{2}-9b^{2}}{a^{2}-6ab + 9b^{2}}$; (6)$\frac {a^{2}-4ab + 4b^{2}}{a^{2}-4b^{2}}$;
(7)$\frac {0.25a - 0.2b}{0.1a + 0.3b}$; (8)$\frac {x^{2}-1}{x^{2}+2x + 1}$;
(9)$\frac {x^{2}-2x + 1}{(x^{2}+1)^{2}-4x^{2}}$; (10)$\frac {x^{3}-6x^{2}-27x}{x^{2}-8x - 9}$.
答案：1. (1)解：$\frac{6ab^{2}}{3a^{2}b}=\frac{3ab \cdot 2b}{3ab \cdot a}=\frac{2b}{a}$
(2)解：$\frac{6a^{4}c^{2}}{9a^{2}b^{2}}=\frac{3a^{2} \cdot 2a^{2}c^{2}}{3a^{2} \cdot 3b^{2}}=\frac{2a^{2}c^{2}}{3b^{2}}$
(3)解：$\frac{2a - 2}{a^{2}-1}=\frac{2(a - 1)}{(a + 1)(a - 1)}=\frac{2}{a + 1}$
(4)解：$\frac{ma + mb - mc}{a + b - c}=\frac{m(a + b - c)}{a + b - c}=m$
(5)解：$\frac{a^{2}-9b^{2}}{a^{2}-6ab + 9b^{2}}=\frac{(a + 3b)(a - 3b)}{(a - 3b)^{2}}=\frac{a + 3b}{a - 3b}$
(6)解：$\frac{a^{2}-4ab + 4b^{2}}{a^{2}-4b^{2}}=\frac{(a - 2b)^{2}}{(a + 2b)(a - 2b)}=\frac{a - 2b}{a + 2b}$
(7)解：$\frac{0.25a - 0.2b}{0.1a + 0.3b}=\frac{(0.25a - 0.2b) × 20}{(0.1a + 0.3b) × 20}=\frac{5a - 4b}{2a + 6b}$
(8)解：$\frac{x^{2}-1}{x^{2}+2x + 1}=\frac{(x + 1)(x - 1)}{(x + 1)^{2}}=\frac{x - 1}{x + 1}$
(9)解：$\frac{x^{2}-2x + 1}{(x^{2}+1)^{2}-4x^{2}}=\frac{(x - 1)^{2}}{(x^{2}+1 + 2x)(x^{2}+1 - 2x)}=\frac{(x - 1)^{2}}{(x + 1)^{2}(x - 1)^{2}}=\frac{1}{(x + 1)^{2}}$
(10)解：$\frac{x^{3}-6x^{2}-27x}{x^{2}-8x - 9}=\frac{x(x^{2}-6x - 27)}{(x - 9)(x + 1)}=\frac{x(x - 9)(x + 3)}{(x - 9)(x + 1)}=\frac{x(x + 3)}{x + 1}=\frac{x^{2}+3x}{x + 1}$
2. 先约分,再求值:$\frac {x^{2}-2xy + y^{2}}{y - x}$,其中$x = 2$,$y = 3$.
答案：解:$\frac{x^{2}-2xy+y^{2}}{y-x}=\frac{-(x-y)^{2}}{x-y}=-(x-y)=y-x$,当$x=2,y=3$时,原式$=y-x=3-2=1.$
