2/3*1+2/5*3+2/7*5+---+2/2005*2003
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2/3*1+2/5*3+2/7*5+---+2/2005*20032/3*1+2/5*3+2/7*5+---+2/2005*20032/3*1+2/5*3+2/7*5+---+2/2005*2003裂
2/3*1+2/5*3+2/7*5+---+2/2005*2003
2/3*1+2/5*3+2/7*5+---+2/2005*2003
2/3*1+2/5*3+2/7*5+---+2/2005*2003
裂项:
2/3*1+2/5*3+2/7*5+---+2/2005*2003
=2(1/3+1/5*3+...+1/2005*2003)
=2*1/2(1-1/3+1/3-1/5+...+1/2003-1/2005)
=1-1/2005
=2004/2005
2/3*1+2/5*3+2/7*5+---+2/2005*2003
=2*(1/1*3+1/3*5+1/5*7+...+1/2003*2005)
=2*1/2*(1-1/3+1/3-1/5+1/5-1/7+...+1/2003-1/2005)
=1-1/2005
=2004/2005
-|-2/3-(+2/3)|-|(-1/5)+(-2/5)| |4/7-2/5|-|3/5-7/9|+|2/9-3/7|
-3/7+3/2+1+-5
1+3+5+7+.+（2n-1)
1/1 -1/3 2/3 -3/3 -2/5 3/5 -4/5 5/5 -1/7 2/7 -3/7 …… 求 98个是多少
3/2 x 5/7 - (-5/7)x5/2 +(-1/2) 除以7/5 等于多少,
按规侓填数5,7,2,5,3,2,1,（ ）
2/1*3+2/3*5+2/5*7+.+2/17*19+2/19*21=?
2/1*3+2/3*5+2/5*7+2/11*13+2/13*15
2/3×1+2/5×3+2/7×5+.+2/2003×2001+2/2005×2003=?
3+5+7+.+(2n+1)=
1、2、3、4、5、6、7
1,2,3,4,5,6,7,
1,2 ,3,4,5,6,7
1+2-3+4-5+6-7
1,2,3,5,7,11.
1+2+3+4+5+6+7
1,2,3,4,5,6,7
1+2+3+4+6+7+5