递等式计算：1-1/6+1/56+1/72+1/90

题目

递等式计算：1-1/6+1/56+1/72+1/90

答案

1-1/6+1/56+1/72+1/90
=1-1/2+1/3+1/7-1/8+1/8-1/9+1/9-1/10
=1-1/2+1/3+1/7-1/10
=31/21-3/5
=(155-63)/105
=92/105