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单词 IntegrationOfFractionPowerExpressions
释义

integration of fraction power expressions


The antiderivatives of every expression containing fraction powers can not be expressed by using elementary functionsMathworldPlanetmath. However, there are after making a substitution.

  • R(x,xr1,,xrm)𝑑x,  where R means a rational function of its arguments.If the common denominator of the fraction power exponentsMathworldPlanetmath rj is n, the substitution

    x:=tn,dx=ntn-1dt

    changes each exponent to an integer and the whole integrand to a rational function in the variable t.

    Example.  For  x12x34+1𝑑x  the least common multiple of the denominators of 12 and 34 is 4, whence we make the substitution  x=t4,  dx=4t3dt.  Then we obtain

    x12x34+1𝑑x= 4t5dtt3+1= 4(t2-t2t3+1)𝑑t= 4(t33-13ln|t3+1|)+C
    =43(x34-ln|x34+1|)+C.
  • In R(x,(ax+bcx+d)r1,,(ax+bcx+d)rm)𝑑x,  correspondently the substitution

    ax+bcx+d:=tn

    changes the integrand to a rational function.

    Example.  For  x+4x𝑑x  we substitute  x+4=t2,  dx=2tdt,  getting

    x+4x𝑑x= 2t2t2-4𝑑t= 2(1+4t2-4)𝑑t= 2t+2ln|t-2t+2|+C
    = 2x+4+2ln|x+4-2x+4+2|+C.

References

  • 1 N. Piskunov: Diferentsiaal- ja integraalarvutus kõrgematele tehnilistele õppeasutustele. Viies, täiendatud trükk.  Kirjastus “Valgus”, Tallinn (1965).
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更新时间:2025/5/4 16:21:14