偶数,奇数求和

2+4+6+8.....+n=(2+n)n/4
1+3+5+7.....+n=(n+1)^2/4

偶数2+4+6+8.....+n的和
2+4+6+8.....+n
=2*(1+2+3+...+n/2)
=(1+n/2)*n/2
=(2+n)*n/4

奇数1+3+5+7.....+n的和
1+3+5+7.....+n
=(n+1)/2+0+2+...+(n-1)
=后面的用前面偶数结论...
=(n+1)/2+(n+1)(n-1)/4
=(n+1)*(n+1)/4

偶数2+4+6+8.....+n=(2+n)+(4+n-2)+(6+n-3)+...=(2+n)*n/4
奇数1+3+5+7.....+n=(1+n)+(3+n-2)+(5+n-3)+...=(1+n)^2/4

1: (2+n)*n/4
2: (n+1)^2/4