BCECE Engineering BCECE Engineering Solved Paper-2013

  • question_answer
    Domain of \[f(x)=y=\sqrt{{{\log }_{3}}\{\cos (\sin x)\}}\]is

    A)  \[\left\{ \frac{n\pi }{2}:n\in l \right\}\]

    B)         \[\{2n\pi :n\in l\}\]

    C)  \[\{n\pi :n\in l\}\]          

    D)         None of the above

    Correct Answer: C

    Solution :

    Here y would assume real values if \[{{\log }_{3}}cos\{(\sin x)\}\ge 0\]\[\Rightarrow \]\[\cos (\sin x)\ge 1\] \[\Rightarrow \]               \[\cos (\sin x)=1\,as-1\le \cos \theta \le 1\] \[\Rightarrow \]               \[\sin x=0\] \[\Rightarrow \]               \[x=n\pi ,n\in l\] Hence, the domain consists of the multiples of \[\pi \]i.e., domain \[(y)=\{n\pi :n\in l\}.\]


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