求Sn=1/1x2+1/2x3+1/3x4+.+1/n(n+1)

求使1x2+2x3+3x4+…+n(n+1) 已知无穷数列1x2,2x3,3x4…,n（n+1）,… 求： 1x2+2x3+3x4+...+n（n+1）=? 求线性方程组 x2-x3-x4=0 x1+x2-x3+3x4=1 x1-x2+x3+5x4=-1 x1+2x2-2x3+ 一道简便计算数学题1X2+2X3+3X4+4X5...+n(n+1)一1X2+2X3+3X4+4X5...+2013X2 1/1x2+1/2x3+1/3x4+...+1/n(n+1)怎么算 1 总体X~N(2,4),X1,X2,X3,X4为样本,则(X1+X2+X3+X4)/4~( ) 数学题目,求速度1x2十2x3+…+100x101=1x2+2x3+…+n（n十1） 1x2x3+2+3x4+…+n(n 求数列1/1x2,1/2x3,1/3x4,1/4x5.的前n项和--- X1+2X2-X3+X4=1 (x1,x2,x3,x4,x5,x6)来自正态总体N(0,1),Y=(x1+x2+x3)^2+(x4)^2+(x5)^2 设X1,X2,X3,X4来自正态分布N(0,1)的简单随机样本,求统计量Y=(X2+X3+X4)^2/3X1^2的服从分