1x2+2x3+3x4+……+19x20如何巧算?
(2X2)/1X3+(4X4)/(3X5)+(6X6)/(5X7)+...+(20X20)/(19X21)==?
计算①1x2/1+2x3/1+3x4/1+```+19x20/1= ②1x4/1+4x7/1+7x10/1+```+91
求线性方程组 x2-x3-x4=0 x1+x2-x3+3x4=1 x1-x2+x3+5x4=-1 x1+2x2-2x3+
已知无穷数列1x2,2x3,3x4…,n(n+1),… 求:
1x2+2x3+3x4+4x5+……+10x11
1x2/1+2x3/1+3x4/1+4x5/1+…+39x40/1
求使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
1x1!+2x2!+3x3!+4x4!.nxn!