高等数学,不定积分?
3个回答
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(1)
let
u = x^(1/6)
du = (1/6) x^(-5/6) dx
dx = 6u^5 du
∫ x^(1/3)/[ x.(x^(1/2) +x^(1/3)) ] dx
=∫ { u^2/[ u^6.(u^3 +u^2) ] } [6u^5 du]
=6∫ du/[u(u +1)]
=6ln|u/(u+1) |+C
=6ln| x^(1/6)/( x^(1/6) +1) | +C
(2)
∫ xarctanx dx
=(1/2)∫ arctanx dx^2
=(1/2)x^2.arctanx -(1/2)∫ x^2/(1+x^2) dx
=(1/2)x^2.arctanx -(1/2)∫ [1 -1/(1+x^2)] dx
=(1/2)x^2.arctanx -(1/2)[x -arctanx] + C
let
u = x^(1/6)
du = (1/6) x^(-5/6) dx
dx = 6u^5 du
∫ x^(1/3)/[ x.(x^(1/2) +x^(1/3)) ] dx
=∫ { u^2/[ u^6.(u^3 +u^2) ] } [6u^5 du]
=6∫ du/[u(u +1)]
=6ln|u/(u+1) |+C
=6ln| x^(1/6)/( x^(1/6) +1) | +C
(2)
∫ xarctanx dx
=(1/2)∫ arctanx dx^2
=(1/2)x^2.arctanx -(1/2)∫ x^2/(1+x^2) dx
=(1/2)x^2.arctanx -(1/2)∫ [1 -1/(1+x^2)] dx
=(1/2)x^2.arctanx -(1/2)[x -arctanx] + C
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