(i) ab – bc, bc – ca, ca – ab (ii) a – b + ab, b – c + bc, c – a + ac

(iii) 2p^q^2 - 3pq + 4, 5+7pq - 3p^2q^2

(iv) l^2 + m^2 , m^2 + n^2 , n^2 + l^2 , 2lm + 2mn + 2nl