Question

1/1x2十1/2x3十l十1/8x9十1/9x1o

Answer 1

裂项法：

1/1x2十1/2x3十……十1/8x9十1/9x10

=1-1/2+1/2-1/3+……+1/8-1/9+1/9-1/10

=1-1/10

=9/10