C(8,0) + C(8,1)/2 + C(8,2)/3 + C(8,3)/4 + C(8,4)/5 +
C(8,5)/6 + C(8,6)/7 + C(8,7)/8 + C(8,8)/9 =
我知道公式
想知道推導過程
想破頭了還是不知道怎麼推出來的...囧
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