1/1×2+1/2×3+1/3×4+∧+1/1999×2000等于?
问题描述：
1/1×2+1/2×3+1/3×4+∧+1/1999×2000等于?
答
1/1×2+1/2×3+1/3×4+.+1/1999×2000
=1/1-1/2+1/2-1/3+1/3-1/4+.+1/1999-1/2000
=1-1/2000
=1999/2000