MCQ
If ${I_n} = \int {{{(\log x)}^n}\,\,dx} ,$ then ${I_n} + n{I_{n - 1}} = $
  • $x{(\log x)^n}$
  • B
    ${(x\log x)^n}$
  • C
    ${(\log x)^{n - 1}}$
  • D
    $n{(\log x)^n}$

Answer

Correct option: A.
$x{(\log x)^n}$
a
(a)${I_n} = \int {{{(\log x)}^n}dx} $ .....$(i)$
$\therefore {I_{n - 1}} = \int {{{(\log x)}^{n - 1}}dx} $.....$(ii)$
Now, ${I_n} = \int {{{(\log x)}^n}.\,dx} = {(\log x)^n}x - n\int {{{(\log x)}^{n - 1}}\frac{1}{x}x\,dx} $
$ = x{(\log x)^n} - n\int {{{(\log x)}^{n - 1}}dx} $
${I_n} = x{(\log x)^n} - n{I_{n - 1}}$; $\therefore {I_n} + n\,{I_{n - 1}} = x{(\log x)^n}$.

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