1+2+3...+n① n個(gè)數(shù),求和 n(n+1)/22+3+4...n+1② 也是n個(gè)數(shù),求和 n(2+n+1)/2①+②=168(n(n+1)+n(n+3))/2 =n(n+2)=168n=123+5+7+…+（2n+1）有n項(xiàng)3+5+7+…+（2n+1）= n(3+2n+1)/2=n(n+2)=168 n=12...我知道這種方法了我只是疑問(wèn)我的方法為什么不對(duì)你n+1的前面還有一個(gè)n. 2+3+4... n+n+1②1+ 2+3+4... n+n=(n(n+1)/2)+n①+②=2(n(n+1)/2)+n=n(n+1)+n=n(n+2)=168n=12？？哪來(lái)的n2+3+4... n+(n+1)②②= 2+3+4...+(n-1)+n+(n+1) =1+2+3+4...+(n-1)+n+n(n+1) 拆開(kāi)后=(1+2+3+4...+(n-1)+n)+n =(n(n+1)/2)+n