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求求数学达人帮帮忙,看不清的加Q824629418
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求求数学达人帮帮忙,看不清的加Q824629418
1.=1-1/7=5/7
2.=1-1/2009=2008/2009
3.=1/5-1/2002=1997/2002
=(1-1/2)+(1/2-1/3)+(1/3-1/4)+。。。。。+(1/2008-1/2009)
=1-1/2+1/2-1/3+1/3-1/4+1/4+。。。。。。+1/2008-1/2009
=1-1/2009
=2008/2009
1.1/2+1/2*3+1/3*4+1/4*5+1/5*6+1/6*7
=1/2+(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+(1/5-1/6)+(1/6-1/7)
=1/2+1/2+-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7
=1-1/7=6/7