factorise:7a5 - 567a
7a5 - 567a
= 7a(a4 - 81)
= 7a (a2)2 - (9)2
= 7a (a2 + 9) (a2 - 9)
= 7a (a2 + 9) ((a)2 - (3)2)
= 7a (a2 + 9) (a + 3)(a - 3)
