6/5-12/7+12/7+20/9-30/11+……+18+19/18×19-19+20/19×20这道题怎么做要简算

题目抄得比较乱,前面的分数都写反了。应该是：5/6 -7/12 +9/20 -11/30+。。。+(18+19)/(18×19)-(19+20)/(19×20)5/6 -7/12 +9/20 -11/30+。。。+(18+19)/(18×19)-(19+20)/(19×20)=(2+3)/(2×3)-(3+4)/(3×4)+(4+5)/(4×5)-(5+6)/(5×6)+。。。+(18+19)/(18×19)-(19+20)/(19×20)=(1/2+1/3)-(1/3+1/4)+(1/4+1/5)-(1/5+1/6)+。。。+(1/18+1/19)-(1/19+1/20)=(1/2+1/3+1/4+1/5+。。。+1/18+1/19)-(1/3+1/4+1/5+1/6+。。。+1/19+1/20)=1/2 -1/20=9/20很简单,化为分子相同,分母小的,分数的值就大。变形：30/78 30/85 30/69 30/6630/66>30/69>30/78>30/85,因此：15/33>10/23>5/13>6/17