一共n-1项原式=（1-1/2）+(1-1/6)+(1-1/12)+(1-1/20)+(1-1/30)+.+( 1-1/n(n-1) )= n-1 -(1/2+1/6+1/12+1/20+1/30+……+1/n(n-1))= n-1 -(1-1/2 + 1/2-1/3 + 1/3-1/4 + 1/4-1/5 + 1/5-1/6 +.+ 1/(n-1)-1/n )= n-1 -(1...