1/1×2+1/2×3+1/3×4+1/4×5+…+1/39×40怎么计算如题

问题描述:

1/1×2+1/2×3+1/3×4+1/4×5+…+1/39×40怎么计算如题

1/1×2+1/2×3+1/3×4+1/4×5+…+1/39×40 =1-1/2+1/2-1/3+1/3-1/4+.+1/39-1/40 =1-1/40 =39/40