已知n∈N,n>1,求证:log n (n+1)>log n+1(n+2)
问题描述:
已知n∈N,n>1,求证:log n (n+1)>log n+1(n+2)
分析法证明
答
要证:log(n)(n+1)>log(n+1)(n+2),
即要证log(n+1)/logn>log(n+2)/log(n+1)(换底公式)
即要证log(n+1)log(n+1)>logNlog(n+2)
而由基本不等式
lognlog(n+2)