解ï¼è¯¦ç»è¿ç¨æ¯ï¼ln[e^x+e^(-x)]丨(x=0,t)=ln[e^t+e^(-t)]-ln2ãèï¼e^t+e^(-t)=[1+e^(2t)]e^(-t)ï¼
â´ln[e^t+e^(-t)]=-t+ln[1+e^(2t)]ãâ´t-ln[e^x+e^(-x)]丨(x=0,t)=2t-ln[1+e^(2t)]+ln2ã
â´lim(tââ){2t-ln[1+e^(2t)]+ln2}=lim(tââ){2t-ln[1+e^(2t)]}+ln2ã
åï¼2t-ln[1+e^(2t)]=ln[e^(2t)]-ln[1+e^(2t)]=ln{e^(2t)/[1+e^(2t)]}=ln{1/[1+e^(-2t)]}ï¼lim(tââ)e^(-2t)=0ï¼
â´lim(tââ){2t-ln[1+e^(2t)]+ln2}=ln2+lim(tââ)ln{1/[1+e^(-2t)]}=ln2ãä¾åèã
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