[理工] 离散 生成函数4-38

楼主: chirahappy (chira)   2018-09-06 10:16:30
想问例30的第二小题
为何 最后面答案后面需要 写其中n>=1
而其他两题不用?
https://i.imgur.com/LZavGS8.jpg
https://i.imgur.com/usOPpHs.jpg
https://i.imgur.com/Raio6wm.jpg

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