这是求值,不是因式分
a(a-1)(a-2)(a-3)(a-4)
=a(a-1)(a-4)(a-2)(a-3)
=a(a^2-5a+4)(a^2-5a+6)
=a[(a^2-5a)^2+10(a^2-5a)+24}
=a[a^4-10a^3+25a^2+10a^2-50a+24]
=a^5-10a^4+35a^3-50a^2+24a