取自然对数得lim(x→∞）ln（π/2-arctanx)/lnx (这是∞/∞型,运用洛必达法则）＝lim(x→∞）-1/(1+x^2)*1/（π/2-arctanx)*x=lim(x→∞）-1/x*1/（π/2-arctanx)(这是0/0型,运用洛必达法则）=lim(x→∞）1/x^2*[-(1...