9a³-12a+3a
=3a(3a²-4a+1)
=3a(a-1)(3a-1)
by⁵-by⁴+by-b
=b(y⁵-y⁴+y-1)
=b[y⁴(y-1)+(y-1)]
=b(y-1)(y⁴+1)