分数加减法、数学题 ,1小时以内

1/1x2+1/2x3+1/3x4+1/4x5+……1/8x9+1/9x10=1-1/2+1/2-1/3+1/3-1/4+。+1/8-1/9+1/9-1/10=1-1/10=9/10 1/1x2=1/2=1-(1/2)1/2x3=1/6=1/2 - 1/3 。1/9x10=1/9-1/10