求证:log以n为底(n+1)>log以(n+1)为底(n+2)

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求证:log以n为底(n+1)>log以(n+1)为底(n+2)

证:logn(n+1)=ln(n+1)/ln(n)=1+ln[(n+1)/n]/ln(n)
log(n+1)(n+2)=1+ln[(n+2)/(n+1)]/ln(n+1)
∵(n+1)/n>(n+2)/(n+1)
∴ln[(n+1)/n]>ln[(n+2)/(n+1)]
又ln(n)log(n+1)(n+2)