1+2+ 3+…+(n+1)=(n+2)(n+1)/2(条).是怎样得到的?
问题描述:
1+2+ 3+…+(n+1)=(n+2)(n+1)/2(条).是怎样得到的?
答
1+2+ 3+…+(n+1)=s
(n+1)+n+……+3+2+1=s两式相加得 (n+1+1)+(n+2)+(n-1+3)+……+(2+n)+(1+n+1)=2s即2s=(n+2)+(n+2)+……+(n+2) (共有n+1个)2s=(n+1)(n+2)∴1+2+ 3+…+(n+1)=s=(n+1)(n+2)/2лл��(^_^)������ô��...