Factorise by grouping method:
a3+a−3a2−3
a3 + a - 3a2 - 3= a (a2 + 1) - 3(a2 + 1)
= (a2 + 1) (a -3).
a4−2a3−4a+8
a2+4b2−3a+6b−4ab
a(a−4)−a+4
y2−(a+b)y+ab