1.1/2>(1/2+1/4+...+1/2n)/n (n>=2)2.1/(n+1)(1+1/3+1/5+,+1/(2n-1))>1/n(1/2+1/4+,+1/2n) (n>=2)

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1.1/2>(1/2+1/4+...+1/2n)/n (n>=2)2.1/(n+1)(1+1/3+1/5+,+1/(2n-1))>1/n(1/2+1/4+,+1/2n) (n>=2)
1.1/2>(1/2+1/4+...+1/2n)/n (n>=2)
2.1/(n+1)(1+1/3+1/5+,+1/(2n-1))>1/n(1/2+1/4+,+1/2n) (n>=2)

1.1/2>(1/2+1/4+...+1/2n)/n (n>=2)2.1/(n+1)(1+1/3+1/5+,+1/(2n-1))>1/n(1/2+1/4+,+1/2n) (n>=2)
(1)两边同乘n
n/2>1/2+1/4+...+1/2^n
右边分子全部用2带(如:1/4n(1-1/2)=n/2>1/2+1/4+,+1/2n(证明方法同第一小题)
得证

这个给你提个醒,用放缩法。我好久都没做这个了~

1. n/2>1/2+1/4+...+1/2n
1/2=n/2/n>(1/2+1/4+...+1/2n)/n
2. n(1/2+1/4+,,+1/2n)=n(1/(1+1)+1/(3+1)+,,+1/(2n-1+1))
so题2左式必小于右式