(2) Their simplest common denominator is (x-y)? a/(y-x)? =a/(x-y)? b/(x-y)(x-y) =b/(x-y)?
(3) Their simplest common denominator is 2 (a-b) 3a/2a-2b = 3a/2 (a-b) 2a/b-a =-4a/2 (a-b).