1.l1/3-1/2l + l1/4-1/3l + l1/5-1/4l +.+ l1/10-1/9l= 2.1/1*2
1.l1/3-1/2l + l1/4-1/3l + l1/5-1/4l +.+ l1/10-1/9l= 2.1/1*2 + 1/2*3 + 1/3*4 +.1/2008*2009= 3.1/2 + (1/3+2/3) + (1/4+2/4+3/4) + (1/5+2/5+3/5+4/5) + .+ (1/60+2/60+3/60+.58/60+59/60)= 4.(1-1/100)* (1-1/101)*(1-1/102)*.*(1-1/2008)= *是乘号 l是绝对值符号