JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2013

  • question_answer
        The maximum value of \[1+\sin \left( \frac{\pi }{4}+\theta  \right)+2\cos \left( \frac{\pi }{4}-\theta  \right)\]for real values of \[\theta \]is

    A)  3                                            

    B)  5

    C)  4                                            

    D)  None of these

    Correct Answer: C

    Solution :

                    \[1+\sin \left( \frac{\pi }{4}+\theta  \right)+2\cos \left( \frac{\pi }{4}-\theta  \right)\] \[=1+\frac{1}{\sqrt{2}}(\cos \theta +\sin \theta )+\sqrt{2}(\cos \theta +\sin \theta )\] \[=1+\left( \frac{1}{\sqrt{2}}+\sqrt{2} \right).(\cos \theta +\sin \theta )\] \[=1+\left( \frac{1}{\sqrt{2}}+\sqrt{2} \right).\sqrt{2}\cos \left( \theta -\frac{\pi }{4} \right)\] \[\therefore \]Maximum value\[=1+\left( \frac{1}{\sqrt{2}}+\sqrt{2} \right).\sqrt{2}=4\]


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