当n=k时,有:
(k)^(k+1)>(k+1)^k 【n^(k+2)表示n的k+2次方】
则当n=k+1时,
(k+1)^(k+2)
=[k^(k+1)]×[(k+1)^(k+2)]/[k^(k+1)]
>[(k+1)^k]×[k+1]×[(k+2)/(k)]^(k+1)
=[(k+1)^(k+1)]×[(k+2)/k]^(k+1)
=[(k+1)×(k+2)/k]^(k+1)
考虑:(k+1)(k+2)/k与k+2的大小,
(k+1)(k+2)-k(k+2)=k+3>0,则:
(k+1)(k+2)-k(k+2)>0,即:(k+1)(k+2)/k>k+2,则:
[(k+1)×(k+2)/k]^(k+1)>(k+2)^(k+1)
也就是说,当n=k+1时成立.