∫xe^xdx√(e^x-2)求不定积分

1个回答

  • ∵∫[xe^x/√(e^x-2)]dx

    =∫x[1/√(e^x-2)]d(e^x-2)

    =2∫xd[√(e^x-2)]

    =2x√(e^x-2)-2∫√(e^x-2)dx.

    ∴令√(e^x-2)=u,则:x=ln(2+u^2),∴dx=2[u/(2+u^2)]du.

    ∴∫[xe^x/√(e^x-2)]dx

    =2x√(e^x-2)-2∫u·2[u/(2+u^2)]du

    =2x√(e^x-2)-4∫{[(2+u^2)-2]/(2+u^2)}du

    =2x√(e^x-2)-4∫du+8∫[1/(2+u^2)]du

    =2x√(e^x-2)-4u+8∫[1/(2+u^2)]du

    =2x√(e^x-2)-4√(e^x-2)+8∫[1/(2+u^2)]du.

    再令u=√2t,则:t=u/√2,du=√2dt.

    ∴∫[xe^x/√(e^x-2)]dx

    =2x√(e^x-2)-4√(e^x-2)+8√2∫[1/(2+2t^2)]dt

    =2x√(e^x-2)-4√(e^x-2)+4√2∫[1/(1+t^2)]dt

    =2x√(e^x-2)-4√(e^x-2)+4√2arctant+C

    =2x√(e^x-2)-4√(e^x-2)+4√2arctan(u/√2)+C

    =2x√(e^x-2)-4√(e^x-2)+4√2arctan√[(1/2)e^x-1]+C.