| 一般項=(-1)^r 1/(r+1) nCr=(-1)^r・1/(r+1)・n(n-1)・・・(n-r+1)/r! =(-1)^r・n(n-1)・・・(n-r+1)/(r+1)! =(-1)^r・1/(n+1)・(n+1)n(n-1)・・・(n-r+1)/(r+1)! =(-1)^r・1/(n+1)・(n+1)C(r+1) =1/(n+1)・(-1)^r・(n+1)C(r+1) ( r=0,1,2,・・・,n) 与式=1/(n+1){(n+1)C1-(n+1)C2+(n+1)C3-・・・+(-1)^n・(n+1)C(n+1)} =1/(n+1){(n+1)C1-(n+1)C2+(n+1)C3+・・・+(-1)^n・(n+1)C(n+1)} =1/(n+1){(n+1)C0-(n+1)C0+(n+1)C1-(n+1)C2+(n+1)C3-・・・+(-1)^n・(n+1)C(n+1)} =1/(n+1){(n+1)C0-[(n+1)C0-(n+1)C1+(n+1)C2-(n+1)C3+・・・+(-1)^(n+1)・(n+1)C(n+1)]} =1/(n+1){(n+1)C0-(1-1)^(n+1)}=1/(n+1){1 - 0^(n+1)}=1/(n+1)
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