a^2+3a+1=0
a^4+a^3-6a^2-5a+5
=a^4+3a^3+a^2-2a^3-7a^2-5a+5
=a^2(a^2+3a+1)-2(a^3+3a^2+a)-a^2-3a+5
=a^2(a^2+3a+1)-2a(a^2+3a+1)-(a^2+3a+1)+6
=0-0-0+6
=6
如果本题有什么不明白可以追问,