n的n+1次方大于(n+1)的n次方 n是大于等于3的自然数

1个回答

  • 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.