求不定积分dx/(x的三次方根+x的二次方根)∫dx/(x的三次方根+x的二次方根)

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求不定积分dx/(x的三次方根+x的二次方根)∫dx/(x的三次方根+x的二次方根)

求不定积分dx/(x的三次方根+x的二次方根)∫dx/(x的三次方根+x的二次方根)
求不定积分dx/(x的三次方根+x的二次方根)
∫dx/(x的三次方根+x的二次方根)

求不定积分dx/(x的三次方根+x的二次方根)∫dx/(x的三次方根+x的二次方根)
既然满足三次方根x,又要满足二次方根x,当然是它们的最小公倍数6
令x = u^6,dx = 6u^5 du
∫ dx / (x^1/3 + x^1/2) dx
= ∫ 6u^5 / [(u^6)^1/3 + (u^6)^1/2] du
= 6∫ u^5 / (u² + u³) du
= 6∫ u³ / (1 + u) du
= 6∫ [u² - u - 1/(u+1) + 1] du
= 6[u³/3 - u²/2 - ln|u+1| + u] + C
= 2u³ - 3u² - 6ln|1+u| + 6u + C
= 2√x - 3x^(1/3) + 6x^(1/6) - 6ln|1+x^(1/6)| + C
PS:x^(1/n)是n次方根x,所以x^(1/6)是6次方根x

令 t = x^(1/6), x^(1/2) = t³, x^(1/3) = t², dx = 6t^5 dt
原式 = ∫ 6t^5 / [t³ + t²]dt = ∫ 6t³/(1+t) dt
= 6 ∫ [t² - t +1 - 1/(1+t) ] dt
= 2t³ - 3t² + 6t - ln(1+t) + C
= 2x^(1/2) - 3x^(1/3) + 6x^(1/6) - ln(1+x^(1/6) ) + C