有理数的减法题 急!1. 3乘5分之一+5乘7分之一+7乘9分之一+····+2007乘2009分之一得多少?要有过程!2. 从1到100这100个正整数中,取出10个数使其倒数的和等于1,求这10个数.要有过程!

39+[-23]+0+[-16]=
[-18]+29+[-52]+60=
[-3]+[-2]+[-1]+0+1+2=
[-301]+125+301+[-75]=
[-1]+[-1/2]+[+3/4]+[-1/4]=
[-7/2]+[+5/6]+[-0.5]+4/5+19/6=
[-26.54]+[-6.14]+18.54+6.14=
1.125+[-17/5]+[-1/8]+[-0.6]=
0.75+[-11/4]+0.125+12又5/7+[-3/8]=
[-4/9]+[-3/5]+[+11/8]+[+5/9]+[-1/8]+[-0.4]=
够吗？

7-(-9)-6-(-10)

1:
1/(3*5)+1/(5*7)+1/(7*9)+...+1/(2007*2009)
==1/2*(1/3-1/5)+1/2(1/5-1/7)+1/2(1/7-1/9)...+1/2(1/2007-1/2009)
=1/2*(1/3-1/5+1/5-1/7+1/7-1/9...+1/2007-1/2009)
=1/2(1/3-1/2009)=1003/6027;
2:
因为
1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10+1/10=1;
所以:
(1-1/2)+(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+(1/5-1/6)+(1/6-1/7)+(1/7-1/8)+(1/8-1/9)+(1/9-1/10)+1/10=1;
所以:
1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90+1/10=1;
所以倒数和为1的十个数分别为2,6,12,20,30,42,56,72,90,10;