JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2012

  • question_answer
        If the first term of an AP is 2 and common difference is 4, then sum of 40 terms is

    A)  3200                     

    B)  1600

    C)  200                       

    D)  2800

    Correct Answer: A

    Solution :

                    Let\[f(x)=6\sin x\cos x+4\cos 2x\]            \[f(x)=3(2\sin x\cos x)+4\cos 2x\] \[\Rightarrow \]\[f(x)=3\sin 2x+4\cos 2x\] We know that maximum and minimum value of the expression, \[a\sin x+b\cos x\]are\[\sqrt{{{a}^{2}}+{{b}^{2}}}\]and\[-\sqrt{{{a}^{2}}+{{b}^{2}}}\] respectively. \[\therefore \]Maximum value of\[f(x)\]                                 \[=\sqrt{9+16}=\sqrt{25}=5\]and minimum value of \[f(x)=-\sqrt{9+16}=-\sqrt{25}=-5\]


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