求不定积分∫e的三次根号x幂dx

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求不定积分∫e的三次根号x幂dx

求不定积分∫e的三次根号x幂dx
求不定积分∫e的三次根号x幂dx

求不定积分∫e的三次根号x幂dx
z³ = x,dx = 3z² dz
∫ e^[x^(1/3)] dx
= 3∫ z²e^z dz = 3∫ z² de^z
= 3z²e^z - 3∫ 2ze^z dz
= 3z²e^z - 6∫ z de^z
= 3z²e^z - 6ze^z + 6∫ e^z dz
= 3z²e^z - 6ze^z + 6e^z + C
= 3[z² - 2z + 2]e^z + C
= 3[x^(2/3) - 2x^(1/3) + 2]e^[x^(1/3)] + C

设x^(1/3) = u
那么x = u^3
dx = 3u^2du
e^(x^(1/3))dx = 3u^2 e^u du
对这个积分得3 E^u (2 - 2 u + u^2)
代入x即可