=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6=1-1/6=5/6
1/1×2+1/2×3+1/3×4+1/4×5+1/5×6=1-1/2+1/2-1/+1/3-1/4+1/4-1/5+1/5-1/6=5/6
5、6
