$$\lim_{x\rightarrow\infty}\left(\frac{\pi}{2}-arctanx\right)^{\frac{1}{\ln x}}=\lim_{x\rightarrow\infty}e^{\ln \left(\frac{\pi}{2}-arctanx\right)^{\frac{1}{\ln x}}}=\lim_{x\rightarrow\infty}e^{{\frac{1}{\ln x}}\ln \left(\frac{\pi}{2}-arctanx\right)}$$
$$=$$
$$\lim_{x\rightarrow\infty}e^{{\frac{\ln \left(\frac{\pi}{2}-arctanx\right)}{\ln x}}}=$$
$$=$$
$$e^{\lim_{x\rightarrow\infty}{{\frac{\ln \left(\frac{\pi}{2}-arctanx\right)}{\ln x}}}}$$
$$=$$
$$\ldots$$
L'Hospital uygulayarak sonucu bulursun.