求证ln(n+1)>1/3+1/5+1/7+.+1/2n+1.............+1/(2n+1)

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求证ln(n+1)>1/3+1/5+1/7+.+1/2n+1.............+1/(2n+1)
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求证ln(n+1)>1/3+1/5+1/7+.+1/2n+1.............+1/(2n+1)
求证ln(n+1)>1/3+1/5+1/7+.+1/2n+1
.............+1/(2n+1)

求证ln(n+1)>1/3+1/5+1/7+.+1/2n+1.............+1/(2n+1)
证明:
记f(x)=ln(1+x)-x/(2+x),x>0
f'(x)=[(x+1)²+1]/[(x+1)(2+x)²]>0,f(x)↑
又f(x)可在x=0处连续则
f(x)>f(0)=0
即 ln(1+x)>x/(2+x)
取1/n(>0)替换x有
ln[(n+1)/n]>1/(2n+1)
将此不等式中的n依次从1取到n累加有
ln(2/1)+ln(3/2)+...+ln[(n+1)/n]>1/3+1/5+...+1/(2n+1)
即 ln(n+1)>1/3+1/5+...+1/(2n+1)
得证.