1/﹙1×2﹚+1/﹙2×3﹚+1/﹙3×4﹚+1/﹙4×5﹚+……+1/﹙8×9﹚+1/﹙9×10﹚
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+……+1/8+1/9+1/9-1/10
=1-1/10
=9/10.