Simplify combining the like terms:
(i) a – (a – b) – b – (b – a)
(ii) x2 – 3x + y2 – x – 2y2
(i) a – (a – b) – b – (b – a)
= a – a + b – b – b + a
= (a – a + a) + (b – b – b)
= a – b
(ii) x2 – 3x + y2 – x – 2y2
= x2 + y2 – 2y2 – 3x – x
= x2 – y2 – 4x