题解 | #等差数列#
等差数列
http://www.nowcoder.com/practice/f792cb014ed0474fb8f53389e7d9c07f
思路
- 等差数列前n项和的公式是关键sn=n*a1+n*(n-1)*d/2
Answer
#include<stdio.h>
int main()
{
int n;
scanf("%d",&n);
printf("%d",n*2+n*(n-1)*3/2);
return 0;
}
等差数列
http://www.nowcoder.com/practice/f792cb014ed0474fb8f53389e7d9c07f
#include<stdio.h>
int main()
{
int n;
scanf("%d",&n);
printf("%d",n*2+n*(n-1)*3/2);
return 0;
}
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