2x2/1x3+4x4/3x5+6x6/5x7+8x8/7x9+10x10/9x11+12x12/11x13 仔细看看 给50啊

巧算：1x2+2x3+3x4+4x5+5x6+6x7...+8x9 x1-x2+x3=1x2-x3+x4=21若x1,x2,x3,x4,x5满足方程组 x3-x4+x5=3x4-x5+x1=4x5-x1+x2=5求x2 x3 x4的值2已知 x1+x4+x6+x7=39 x2+x4+x5+x7=49 x3+x5+x6+x7=41 x4+x7=13 x5+x7=14 x6+x7=9 x1+x2+x3+x4+x5+x6+x7=9求x7的值若x1,x2,x3,x4,x5满足方程组 x1-x 1x2+2x3+3x4+4x5+5x6---+99x100=? 1x2+2x3+3x4+4x5+5x6+.+99x100 1/1x2+2/1x3+3/1x4+4/1x5+5/1x6+6/1x7= 1x2+2x3+3x4+4x5+5x6+6x7+7x8+8x9+9x10+10x11 (2X2)/1X3+(4X4)/(3X5)+(6X6)/(5X7)+...+(20X20)/(19X21)==? 1x2+2x3+3x4+4x5+5x6+6x7+7x8+8x9= 1x1-2x2+3x3-4x4+5x5-6x6.-100x100+101x101简便算法答案 1/1x2+1/2x3+1/3x4+1/4x5+1/5x6+......1/2008x2009 2013/1x2+2013/2X3+2013/3X4+2013/4X5+2013/5X6简便计算, =x1,x2,x3,x4,x5,x6都是正数,且（x2x3x4x5x6）÷X1=1,（x1x3x4x5x6）÷x2=2,（x1x2x4x5x6）÷x3=3,（x1x2x3x5x6）÷x4=4,（x1x2x3x4x6）÷x5=6,（x1x2x3x4x5）÷x6=9,求x1+x2+x3+x4+x5+x6=______.是求五个数的和,不是积话说，我的资 计算：1/1x2+1/2x3+1/3x4+1/4x5+1/5x6+1/6x7+1/7x8+1/8x9+1/9x10. 1/1x2+1/2x3+1/3x4+1/4x5+1/5x6+1/6x7+1/7x8 1x2分之1+2x3分之1+3x4分之1+4x5分之1+5x6分之1+6x7分之1 等几? 1/1X2-5/2X3+1/3X4-19/4X5+1/5X6-41/6X7这个题目怎么做 1x2+2x3+3x4+4x5+5x6+6x7+7x8+.+nx（n+1） 要公式,别搞太深奥! 1x2+2x3+3x4+4x5+5x6+6x7+7x8+8x9+9x10+10x11+ +nx(n+1)=