Question
$$\int {\frac{{\sqrt x }}{{1 + \root 4 \of {{x^3}} }}dx} $$ is equal to :
A.
$$\frac{4}{3}\left[ {1 + {x^{\frac{3}{4}}} + \log \left( {1 + {x^{\frac{3}{4}}}} \right)} \right] + C$$
B.
$$\frac{4}{3}\left[ {1 + {x^{\frac{3}{4}}} - \log \left( {1 + {x^{\frac{3}{4}}}} \right)} \right] + C$$
C.
$$\frac{4}{3}\left[ {1 - {x^{\frac{3}{4}}} + \log \left( {1 + {x^{\frac{3}{4}}}} \right)} \right] + C$$
D.
None of these
Answer :
$$\frac{4}{3}\left[ {1 + {x^{\frac{3}{4}}} - \log \left( {1 + {x^{\frac{3}{4}}}} \right)} \right] + C$$
Solution :
$$\eqalign{
& {\text{Put }}x = {z^4}\, \Rightarrow dx = 4{z^3}dz \cr
& \therefore \,\int {\frac{{\root 2 \of x }}{{1 + \root 4 \of {{x^3}} }}dx} \cr
& = \int {\frac{{{z^2}.4{z^3}}}{{1 + {z^3}}}dz} \cr
& = 4\int {\frac{{{z^3}.{z^2}}}{{{z^3} + 1}}dz} \cr
& = \frac{4}{3}\int {\frac{{\left( {y - 1} \right)}}{y}dy\,\,\,\,\,\,} \left[ {{\text{Putting }}{z^3} + 1 = y \Rightarrow {z^2}dz = \frac{1}{3}dy} \right] \cr
& = \frac{4}{3}\left( {y - \log \,y} \right) + C \cr
& = \frac{4}{3}\left[ {1 + {x^{\frac{3}{4}}} - \log \left( {1 + {x^{\frac{3}{4}}}} \right)} \right] + C \cr} $$