初一数学-业主生活–手机房天下问答

共3个回答

麻坛大班丨Lv 3

数列有下面的规律：a(1) = 1a(2) = a(1) + 2a(3) = a(2) + 3…………a(n-1) = a(n-2) + n-1a(n) = a(n-1) + n注：括号内是下标将上述n项相加得a(1) + a(2) + a(3) + …… + a(n-1) + a(n)= a(1) + a(2) + a(3) + …… + a(n-1) + 1+2+3+……+(n-1)+n化简得a(n) = 1+2+3+……+(n-1)+n = (n+1)*n/2通项公式是(n+1)*n/2

+10 2008-08-20 举报
房教授丨Lv 4

把原数列扩大2倍变成2,6,12,20,30,......这样新数列的规律是:1x2,2x3,3x4,4x5,5x6,....,n(n+1).所以原数列规律是:n(n+1)/2

+10 2008-08-20 举报
知书丨Lv 3

n1:1=1n2:3=1+2n3:6=1+2+3n4:10=1+2+3+4n5:15=1+2+3+4+5...nn:n*(1+n)/2=1+2+3+...+(n-1)+n

+10 2008-08-20 举报