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Q. $ \int{{{e}^{\sin \theta }}[\log \sin \theta +\cos e{{c}^{2}}\theta ]}\cos \,\theta d\theta $ is equal to

KEAMKEAM 2008Integrals

Solution:

Let $ I=\int{{{e}^{\sin \theta }}\log \sin \theta \cos \theta d\theta } $
$ +\int{{{e}^{\sin \theta }}\cos e{{c}^{2}}\theta \cos \theta d\theta } $ Put $ \sin \theta =t\Rightarrow \cos \theta d\theta =dt $
$ \therefore $ $ I=\int{{{e}^{t}}\log t\,dt+\int{\frac{{{e}^{t}}}{t}dt}}+\frac{{{e}^{t}}{{t}^{-1}}}{-1}-\int{\frac{{{e}^{t}}{{t}^{-1}}}{-1}}dt $
$={{e}^{t}}\left( \log t-\frac{1}{t} \right)+c $
$={{e}^{\sin \theta }}(\log \sin \theta -\cos ec\theta )+c $