问题标题：
几道数学题-3/1*2+5/2*3-7/3*4+9/4*5-11/5*6+13/6*7-.+2005/1002*1003=1+1/2-2-5/6+3+1/12-4-19/20-5-1/30+6+41/42-7-1/56+8+71/72-9-1/90=
问题描述：
几道数学题
-3/1*2+5/2*3-7/3*4+9/4*5-11/5*6+13/6*7-.+2005/1002*1003=
1+1/2-2-5/6+3+1/12-4-19/20-5-1/30+6+41/42-7-1/56+8+71/72-9-1/90=
邓述珍回答：
1.
3/1*2=1+1/2
5/2*3=1/2+1/3
……
2005/1002*1003=1/1002+1/1003
因此,原式=-1+1/1003=-1002/1003
2.
原式=(1-2+3-4-5+6-7+8-9)+(1/2-5/6+1/12-19/20-1/30+41/42-1/56+71/72-1/90)
=-9+(1/2+1/6+1/12+1/20-1/30-1/42-1/56-1/72-1/90)
=-9+(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))
=-9+(1-1/5-1/5+1/10)
=-8.3
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