几道初一有理数计算题.

1.(1/3-7/12+9/20-11/30+13/42-15/56)*8*21
=56-42+378/5-308/5+52-45
=14+70/5+7
=35
2.1/2+(1/3+2/3)+(1/4+2/4+3/4)+(1/5+2/5+3/5+4/5)+...+(1/2008+2/2008+.+2007/2008)
=1/2+(1/3+2/3)+((1/4+3/4)+2/4)+((1/5+4/5)+(2/5+3/5))+...+((1/2008+2007/2008)+(2/2008+2006/2008)+.)
=1/2+(1)+(1+2/4)+(1+1)+...+(1+1+1...)
=(1/2)*2007+(2007*2006)*(1/2)/2
=2007/2+(2007*1003)/2
=(2007/2)*(1+1003)
=(2007/2)*1004
=2007*502
=1007514
3.1又1/2+2又1/4+3又1/8+.+8又1/256
=(1+2+3+...+8)又（1/2+1/4+1/8+...+1/256)
=36又((128+64+32+16+8+4+2+1)/256)
=36又(255/256)