Question
$$\int {32{x^3}{{\left( {\log \,x} \right)}^2}dx} $$ is equal to :
A.
$$8{x^4}{\left( {\log \,x} \right)^2} + C$$
B.
$${x^4}\left\{ {8{{\left( {\log \,x} \right)}^2} - 4\left( {\log \,x} \right) + 1} \right\} + C$$
C.
$${x^4}\left\{ {8{{\left( {\log \,x} \right)}^2} - 4\left( {\log \,x} \right)} \right\} + C$$
D.
$${x^3}\left\{ {{{\left( {\log \,x} \right)}^2} - 2\left( {\log \,x} \right)} \right\} + C$$
Answer :
$${x^4}\left\{ {8{{\left( {\log \,x} \right)}^2} - 4\left( {\log \,x} \right) + 1} \right\} + C$$
Solution :
$$\eqalign{
& {\text{Let }}I = \int {32{x^3}{{\left( {\log \,x} \right)}^2}dx} \cr
& = 32\left\{ {{{\left( {\log \,x} \right)}^2}\frac{{{x^4}}}{4} - \int {2\,\log \,x\frac{1}{x}.\frac{{{x^4}}}{4}dx} } \right\} \cr
& = \frac{{32}}{4}{x^4}{\left( {\log \,x} \right)^2} - 16\int {{x^3}\log } \,x\,dx \cr
& = 8{x^4}{\left( {\log \,x} \right)^2} - 4{x^4}\log \,x + 4\int {{x^3}dx} \cr
& = {x^4}\left\{ {8{{\left( {\log \,x} \right)}^2} - 4\,\log \,x + 1} \right\} + C \cr} $$