（1）
1/2+1/6+1/12+1/20+1/30+....+1/72+1/90 = 1/1*2 +1/2*3 +1/3*4 +...+1/8*9 +1/9*10 = (1/1 -1/2)+(1/2 -1/3)+...+(1/8 -1/9)+(1/9 -1/10) = 1/1 -1/10 = 9/10 (2)两个绝对值互为相反数，则各自为0
1/2+1/6+1/12+1/20+1/30+....+1/72+1/90 = 1/1*2 +1/2*3 +1/3*4 +...+1/8*9 +1/9*10 = (1/1 -1/2)+(1/2 -1/3)+...+(1/8 -1/9)+(1/9 -1/10) = 1/1 -1/10 = 9/10
所以 ab-2=0 b-1=0
则a=2 b=1
等式为
1/2+1/2-1/3+1/3-1/4+……+1/2013-1/2014=1-1/2014=2013/2014
