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单词 ASpecialCaseOfPartialIntegration
释义

a special case of partial integration


In determining the antiderivative of a transcendental (http://planetmath.org/AlgebraicFunction) functionMathworldPlanetmath U whose derivative U is algebraic (http://planetmath.org/AlgebraicFunction), the result can be obtained when choosing in the formula

UV𝑑x=UV-VU𝑑x

of integration by parts  V1;  then one has

U𝑑x=U1𝑑x=Ux-xU𝑑x.

The functions U in question are mainly the logarithmMathworldPlanetmath (http://planetmath.org/NaturalLogarithm2), the cyclometric functions and the area functions.

Examples.

  1. 1.

    lnxdx=xlnx-x1x𝑑x=xlnx-x+C

  2. 2.

    arcsinxdx=xarcsinx-x11-x2𝑑x=xarcsinx+12-2x1-x2𝑑x=xarcsinx+1-x2+C

  3. 3.

    arctanxdx=xarctanx-x11+x2𝑑x=xarctanx-122x1+x2𝑑x=xarctanx-12ln(1+x2)+C=xarctanx-ln1+x2+C

  4. 4.

    arcoshxdx=xarcoshx-x1x2-1𝑑x=xarcoshx-x2-1+C

The choice  V1  works as well in such cases as  (lnx)2𝑑x  and  ln(lnx)𝑑x,  giving respectively  x((lnx)2-2lnx+2)+C  and  xln(lnx)-Lix+C (see logarithmic integralDlmfDlmfMathworldPlanetmathPlanetmath). Also (arcsinx)2𝑑x  , requiring two integrations by parts, and giving the result  x(arcsinx)2+21-x2arcsinx-2x+C.

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更新时间:2025/5/4 20:20:35