回答：
#1/6 ln | {sqrt（x ^ 3 + 4）-2} / {sqrt（x ^ 3 + 4）+2} | + C#
说明：
替代 #的x ^ 3 + 4 = U ^ 2#。然后 #3倍^ 2DX = 2udu#， 以便
#dx / {x sqrt {x ^ 3 + 4}} = {2udu} / {3x ^ 3u} = 2/3 {du} /（u ^ 2-4）= 1/6（{du} / {u -2} - {杜} / {U + 2}）#
从而
#int dx / {x sqrt {x ^ 3 + 4}} = 1/6 int（{du} / {u-2} - {du} / {u + 2}）= 1/6 ln | {u- 2} / {U + 2} | + C#
#= 1/6 ln | {sqrt（x ^ 3 + 4）-2} / {sqrt（x ^ 3 + 4）+2} | + C#
