Factorise
(i) 6ab - b2 + 12ac - 2bc
(ii) x2 + y - xy - x
(iii) x3 - 2x2y + 3xy2 - 6y3
(iv) a(a + b - c) – bc
(i) 6ab - b2 + 12ac - 2bc
= (6ab - b2) + (12ac - 2bc)
= b(6a - b) + 2c(6a - b)
= (6a - b) (b + 2c)
(ii) x2 + y - xy - x
= x2 - xy - x + y
= x(x - y) - (x - y)
= (x - y) (x - 1)
(iii) x3 - 2x2y + 3xy2 - 6y3
= (x3 - 2x2y) + (3xy2 - 6y3)
= x2(x - 2y) + 3y2(x - 2y)
= (x - 2y) (x2 + 3y2)
(iv) a(a + b - c) - bc
= a2 + ab - ac - bc
= a(a + b) - c(a + b)
= (a + b) (a - c)