Integral Calculus Question 407

Question: $ \int_{{}}^{{}}{\frac{\tan (\log x)}{x}\ dx=} $

Options:

A) $ \log \cos (\log x)+c $

B) $ \log \sin (\log x)+c $

C) $ \log \sec (\log x)+c $

D) $ \log cosec(\log x)+c $

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Answer:

Correct Answer: C

Solution:

Put $ \log x=t\Rightarrow \frac{1}{x}dx=dt $ , therefore $ \int_{{}}^{{}}{\frac{\tan (\log x)}{x}dx=\int_{{}}^{{}}{\tan t\ dt}} $ $ =\log \sec t+c=\log \ \sec (\log x)+c $ .