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I see you also used that by L'Hôpital's rule, \begin{eqnarray*} \lim_{x\to\infty} x^2(\ln x-\ln(x-1))-x &=& \lim_{x\to\infty} \frac{\ln x- \ln(x-1)-1/x}{1/x^2} \\ &=&\lim_{x\to\infty} \left(\frac1x- \frac1{x-1}+\frac1{x^2} \right)\bigg/\left(-2/x^3\right)\\ &=&\lim_{x\to\infty} \left(\frac{1}{x^2(x-1)} \right)\bigg/\left(2/x^3\right)=1/2. \end{eqnarray*}