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令t=ln(x+1);å¯å¾x=e^t-1;
æ以dx=e^tdt=d(e^t);
æ以åå¼=t*e^tdt/((e^t-1)^2+1);
ç±äº
e^tdt/((e^t-1)^2+1)=d(arctan(e^t-1));
ç±dx/(x^2+1)=d(arctanx);
æ以ç±åæ¥ç§¯åæ:
åå¼=t*d(arctan(e^t-1))
=t*arctan(e^t-1)-arctan(e^t-1)dt=t*arctan(e^t-1)-arctan(e^t-1)/e^td(e^t-1)
ä¸é´è¦æ±ä¸ä¸ªåæ£åçä¸å®ç§¯åï¼å¯ä»¥å©ç¨åæ¥ç§¯å æ³ï¼è¿éç´æ¥ç¨:
arctan(x)dx=x*arctanx-ln(x^2+1)/2
æ以æåå¼=t*arctan(e^t-1)-((e^t-1)*arctan(e^t-1)-ln((e^t-1)^2+1)/2)/e^t;
æt=ln(x+1)代åï¼æè
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