规律:1/n(n-1)=1/n-1/(n+1)(1)原式=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5=1-1/5=4/5(2)原式=1/1x2+1/2x3+1/4x5+1/5x6+1/6x7=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7=1-1/7=6/7