Rút gọn: (x+2y).(x2-2xy+4y2)-(x-y).(x2+xy+y2)

Bài 1. Rút gọn
a, (x+2y).($x^2$-2xy+4$y^2$)-(x-y).($x^2$+xy+$y^2$)
b, $(x+1).{(x-1)}^2$-(x+2).($x^2$-x+4)