(1)1-a/a*a-2a+1 (2)3x-4y/8xy-6x*x (3)2x*xy(x-y)/12xy*y(y-x)

(1)
(1-a)/(a^2-2a+1)
=(1-a)/(1-a)^2
=1/(1-a)
(2)
(3x-4y)/(8xy-6x^2)
=(3x-4y)/[2x(4y-3x)]
=-1/(2x)
(3)
2x^2y(x-y)/[12x^2(y-x)]
=-y[2x^2(y-x)]/{6[2x^2(y-x)]
=-y/6
(4)
(a^2-9)/(a^2-2a-3)
=[(a+3)(a-3)][(a-3)(a+1)]
=(a+3)/(a+1)
(5)
题目有问题.
(10a^2-43ab-9b^2)/(10ab+2b^2)
=[(2a-9b)(5a+b)][2b(5a+b)]
=(2a-9b)/(2b)