1/1*5,1/3*7,1/5*9,1/7*11的前N项和

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1/1*5,1/3*7,1/5*9,1/7*11的前N项和
1/1*5,1/3*7,1/5*9,1/7*11的前N项和

1/1*5,1/3*7,1/5*9,1/7*11的前N项和
该数列通项公式为1/（2n-1）*(2n+3),1/1*5+1/3*7+1/5*9+1/7*11……可以写成1/4（1/1-1/5+1/3-1/7+1/5-1/9+1/7-1/11……）这样就可以看出规律了.当N=1时,S1=1/5,当N>=2时,Sn=1/4(1/1+1/3-1/(2n+1)-1/(2n+3)).

(1+1/3+1/5+1/7)*(1/3+1/5+1/7+1/9)-(1+1/3+1/5+1/7+1/9)*(1/3+1/5+1/7) 简算(1+1/3+1/5+1/7)*(1/3+1/5+1/7+1/9)-(1+1/3+1/5+1/7+1/9)*(1/3+1/5+1/7) 简便计算 简算:1/1*3+1/3*5+1/5*7+1/7*9+1/9*11 (1*3)/1+(3*5)/1+(5*7)/1+(7*9)/1+(9*11)/1 1/1*3+1/3*5+1/5*7+1/7*9+1/9*11 (1*3)/1+(3*5)/1+(5*7)/1+(7*9)/1+(9*11)/1 (1/3+1/5+1/7)*(1/5+1/7+1/9)-(1/3+1/5+1/7+1/9)*(1/5+1/7)=? 1/1*3+1/1*3*5+1/1*3*5*7+1/1*3*5*7*9-73/945 1+1+3+5+7+9 1/1*3+1/3*5+1/5*7+1/7*9+...1/17*19= 计算1/(1×3)+1/(3×5)+1/(5×7)+1/(7×9)+.+1/(19×21) 1/1×3+1/3×5+1/5×7+1/7×9+.+1/2013×2015 1/1*3+1/3*5+1/5*7+1/7*9+.+1/101*103 帮帮忙1/1*3+1/3*5+1/5*7+1/7*9+...1/99*101 1/1*3+1/3*5+1/5*7+1/7*9+1/49*51= 计算：1/1×3+1/3×5+1/5×7+1/7×9``````+1/2001×2003 1/1*3+1/3*5+1/5*7+1/7*9+.+1/49*51 1/1*3+1/3*5+1/5*7+1/7*9+...+1/2007*2009=? 1/1*3+1/3*5+1/5*7+1/7*9+.+1/2003*2005