∫ x2/(1+x?) dx =(1/2)∫ (x2-1+x2+1)/(1+x?) dx =(1/2)∫ (x2-1)/(1+x?) dx + (1/2)∫ (x2+1)/(1+x?) dx 分子分母同除以x2 =(1/2)∫ (1-1/x2)/(x2+1/x2) dx + (1/2)∫ (1+1/x2)/(x2+1/x2) dx 分子放到微分之后,然后分母凑个2出来 =(1/2)∫ 1/(x2+1/x2+2-2) d(x+1/x) + (1/2)∫ 1/(x2+1/x2-2+2) d(x-1/x) =(1/2)∫ 1/[(x+1/x)2-2] d(x+1/x) + (1/2)∫ 1/[(x-1/x)2+2] d(x-1/x) =(√2/8)ln|(x+1/x-√2)/(x+1/x+√2)| + (√2/4)arctan[(x-1/x)/√2] + C =(√2/8)ln|(x2+1-√2x)/(x2+1+√2x)| + (√2/4)arctan[(x-1/x)/√2] + C
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