1/2x5 +1/5x8 +1/8x11+……+1/2009x2012=?

裂项法1/2X5+1/5x8+1/8x11.1/2009x2012=? 2x5/1+5x8/1+8x11/1+.2006x2009/1+2009x2012/1 用裂项法计算 1/2x5+1/5x8+1/8x11+.+1/32x35 1/2x5+1/5x8+1/8x11+…………+1/2003x2006+1/2006x2009 = 这是我儿子的小学作业 求前n项和1.1/(2X5),1/(5X8),1/(8X11)...2.2＾2/(1X3),4＾2/(3X5),6＾2/ 1/2x4+1/4x6+1/6x8+…+1/2010x2012 怎么算! 求数列1/2x5,1/5x8,1/8x11...,1/(3n-1)(3n+2)...的前n项和 2x2/1x3+4x4/3x5+6x6/5x7+8x8/7x9+10x10/9x11+12x12/11x13 仔细看看 2X4分之一+4X6分之一+6X8分之一+…+2010X2012分之一= n(n+1)分之一＝ 因式分解:X15+X14+X13+X12+X11+X10+X9+X8+X7+X6+X5+X4+X3+X2+X+1 1x2+2x3+3x4+4x5+……+10x11 2/1x3+2/3X5+2/5x7=2/7x9+2/9x11