谁能帮我讲这道题?1/2+1/6+1/12+1/2

谁能帮我讲这道题?1/2+1/6+1/12+1/20.前三十项的和

2个回答

1/(1×2)+1/(2×3)+1/(3×4)+……+1/(30×31)
=1-1/2+1/2-1/3+1/3-1/4+……+1/30-1/31
=1-1/31
=30/31