(1/2+1/3+...+1/2009)(1+1/2+1/3+...+1/2008)-(1+1/2+...+1/2009)(1/2+1/3+...1/2008)

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(1/2+1/3+...+1/2009)(1+1/2+1/3+...+1/2008)-(1+1/2+...+1/2009)(1/2+1/3+...1/2008)
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(1/2+1/3+...+1/2009)(1+1/2+1/3+...+1/2008)-(1+1/2+...+1/2009)(1/2+1/3+...1/2008)
(1/2+1/3+...+1/2009)(1+1/2+1/3+...+1/2008)-(1+1/2+...+1/2009)(1/2+1/3+...1/2008)

(1/2+1/3+...+1/2009)(1+1/2+1/3+...+1/2008)-(1+1/2+...+1/2009)(1/2+1/3+...1/2008)
令a=1/2+1/3+...+1/2008
原式=(a+1/2009)(1+a)-(1+a+1/2009)a
=a(1+a)+1/2009(1+a)-a(1+a)-1/2009a
=1/2009(1+a)-1/2009a
=1/2009+1/2009a-1/2009a
=1/2009

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  • 令a=1/2+1/3+...+1/2008
    原式=(a+1/2009)(1+a)-(1+a+1/2009)a
    =a(1+a)+1/2009(1+a)-a(1+a)-1/2009a
    =1/2009(1+a)-1/2009a
    =1/2009+1/2009a-1/2009a
    =1/2009

(1/2+1/3+...+1/2009)(1+1/2+1/3+...+1/2008)-(1+1/2+...+1/2009)(1/2+1/3+...1/2008)=
(1/2+1/3+...+1/2009)+(1/2+1/3+...+1/2009)(1/2+1/3+...+1/2008)-(1/2+1/3+...1/2008)-
(1/2+...+1/2009)(1/2+1/3+...1/2008)=1/2009