CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2004

  • question_answer
    If\[f(x)=cos\text{ }x-co{{s}^{2}}x+co{{s}^{3}}x-...\text{ }to\text{ }\infty ,\]then\[\int{f(x)}\,dx\]equals to:

    A)  \[\tan \frac{x}{2}+c\]                   

    B)  \[x+\tan \frac{x}{2}+c\]

    C)  \[x-\frac{1}{2}\tan \frac{x}{2}+c\]

    D)         \[\frac{x-\tan \frac{x}{2}}{2}+c\]

    E)  \[x-\tan \frac{x}{2}+c\]

    Correct Answer: E

    Solution :

    \[f(x)=\cos x-{{\cos }^{2}}x+{{\cos }^{3}}x-\infty \] \[=\frac{\cos x}{1+\cos x}\] \[\therefore \]\[\int{f(x)}dx=\int{\frac{1+\cos x}{1+\cos x}}dx\]                                 \[-\int{\frac{1}{1+\cos x}}dx\]                 \[=x-\frac{1}{2}\tan \frac{x}{2}.2+c\]                 \[=x-\tan \frac{x}{2}.2+c\]


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