Question

1+2+3+4+5+4+3+2+1=25 这个式子用字母表示规律

Answer 1

1+2+3+……+（N-1）+N+（N-1）+……+3+2+1=N²

Answer 2

n+(n+1)+(n+2)+(n+4)+(n+3)+(n+2)+(n+1)+n
=2n+2(n+1)+2(n+2)+2(n+3)+(n+4)
=2n+2n+2+2n+4+2n+6+n+4
=9n+16