1/1×2+1/2×3+1/3×4+···+1/2009×2010·=1-1/2+1/2-1/3+1/3-1/4+……+1/2009-1/2010=1-1/2010=2009/2010
原式=1-1/2+1/2-1/3+1/3-1/4+……+1/2009-1/2010=1-1/2010=2009/2010
1-1/2+1/2-1/3+1/3-1/4+.....+1/2009-1/2010=1-1/2010=2009/2010