1/1x2+1/2x3+1/3x4+...+1/nx(n+1)=_____
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1/1x2+1/2x3+1/3x4+...+1/nx(n+1)=_____
![1/1x2+1/2x3+1/3x4+...+1/nx(n+1)=_____](/uploads/image/z/19619543-47-3.jpg?t=1%2F1x2%2B1%2F2x3%2B1%2F3x4%2B...%2B1%2Fnx%28n%2B1%29%3D_____)
裂项相消法.
1/(1*2)+1/(2*3)+1/(3*4)+.+1/[n(n+1)]
=(1-1/2)+(1/2-1/3)+(1/3-1/4)+.+[1/n-1/(n+1)]
=1-1/(n+1)
=n/(n+1)
填:n/(n+1)
1/(1*2)+1/(2*3)+1/(3*4)+.+1/[n(n+1)]
=(1-1/2)+(1/2-1/3)+(1/3-1/4)+.+[1/n-1/(n+1)]
=1-1/(n+1)
=n/(n+1)
填: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+
X1+2X2-X3+X4=1
1x2+2x3+3x4+...+n(n+1)=?
求齐次线性方程组x1+2x2+x3+x4+x5=1 2x1+4x2+3x3+x4+x5=2 -x1-2x2+x3+3x4
设线性方程组(x1+2x2-2x3+2x4=2,x2-x3-x4=1 x1+x2-x3+3x4=a)
具体写出方程组:2x1+x2-x3+x4=1;x1+2x2+x3-x4=2;x1+x2+2x3+x4=3的通解
解方程组X2+X3+X4=1 X1+X2+X3=5 X3+X4+X5=-5 X4+X5+X1=-3 X5+X1+X2=2
一道简便计算数学题1X2+2X3+3X4+4X5...+n(n+1)一1X2+2X3+3X4+4X5...+2013X2
1+2x4-(x2+2x3)
1 总体X~N(2,4),X1,X2,X3,X4为样本,则(X1+X2+X3+X4)/4~( )
1分解因式:2x4-x3-13x2-15=?2.分解因式:x5+x4+x3+x2+x+1=?3分解因式:x4-4x2+6
求非齐次线性方程组:2x1-x2+4x3-3x4=-4;x1+x3-x4=-3;3x1+x2+x3=1;7x1+7x3-