a) a (x-2y)/b (-(x-2y)=-a/b
б)5x (x-y)/x^3 (-x-y)=-5x/x^3=-5/X^2
в) 3(a-12)/b (-(a-12)=-3/b
г) 7b (1-2b)/21b (-1-2b)=7b/21b=-1/3
д) (5-а)(5+а)/3 (а-5)= -(а-5)(5+а)/3 (а-5)=-5+а/3
е)-3 (х-1)/х-1=-3
-8 (a+b)(a-b)/(a-b)^2=-8 (a+b)/a-b
з) b^3-6b^2+12b-8/(2-b)^2