计算:(1-1/2x2)(1-1/3x3)(1-1/4x4)...(1-1/nxn)(n是正整数)
1x1!+2x2!+3x3!+4x4!.nxn!
1x1 2x2 3x3 4x4 5x5```````nxn有什么规律
1+2x4-(x2+2x3)
设线性方程组(x1+2x2-2x3+2x4=2,x2-x3-x4=1 x1+x2-x3+3x4=a)
数学数列累加求和已知n!=1X2X3X4X.Xn,求1X1!+2X2!+3X3!+4X4!+.+nXn!=?
已知无穷数列1x2,2x3,3x4…,n(n+1),… 求:
1x2+2x3+3x4+...+n(n+1)=?
1x1+2x2+3x3+----+nxn=?
一道简便计算数学题1X2+2X3+3X4+4X5...+n(n+1)一1X2+2X3+3X4+4X5...+2013X2
求线性方程组X1+2X2+3X3+.+nXn=n(n+1)/2的通解
求解一个方程急 X(1次方)+X2+X3=5 X2+X3+X4=1 X3+X4+X5=-5 X4+X5+X1=-3 X5
设X1,X2,X3,X4,X5,X6是来自总体N(0,1)的样本,为什么X1+X2+X3~N(0,3)?