家访案例心得:求证一道数学归纳法的证明题

来源:百度文库 编辑:高考问答 时间:2024/04/24 11:46:41
1·n+2(n-1)+...+(n-1)2+n·1=1/6·n(n+1)(n+2)

1·n+2(n-1)+...+(n-1)2+n·1=1/6·n(n+1)(n+2)
a1=n=1=1/6*1*2*3
a2=3n-2=4=1/6*2*3*4
a3=6n-8=10=1/6*3*4*5
……
an=1/6*n(n+1)(n+2)
an+1=1·(n+1)+2n+...+2n+(n+1)·1
=n+1+2(n-1)+2+3(n-2)+3+……+2(n-2)+2+n+1
=1/6*n(n+1)(n+2)+(1+2+3+……+2+1)
=1/6*n(n+1)(n+2)+1/2*(n+1)(n+2)
=1/6*(n+1)(n+2)(n+3)
原题得证