3/(x²-1)(x-2) = 3/(x-1)(x+1)(x-2) ; 2/(1-x)(x-2) = -2(x+1)/(x-1)(x+1)(x-2);a+b+c/(a-b)(b-c)(c-a) = a+b+c/(a-b)(b-c)(c-a); b/(b-a)(b-c)(a-c) = b/(a-b)(b-c)(c-a).