a^4-4a^2-4a-1
问题描述：
a^4-4a^2-4a-1
答
a^4-4a^2-4a-1
=(a^2-1)(a^2+1)-4a(a+1)
=(a^2+1)(a-1)(a+1)-4a(a+1)
=(a+1)[(a^2+1)(a-1)-4a]