5n的n次方—2a的n次方-8a的n+1次方+6a的n次方—a的n+1次方
题目有误,如是
5a的n次方—2a的n次方-8a的n+1次方+6a的n次方—a的n+1次方
=5a^n-2a^n-8a^(n+1)+6a^n-a^(n+1)
=9a^n-9a^(n+1)