a^2n+1+8a^n+1-9a
问题描述：
a^2n+1+8a^n+1-9a
十字相壮乘法
答
a^2n+1+8a^n+1-9a
=a(a^2n+8a^n-9)
=a(a^n+9)(a^n-1)
1 9
1 -1