KVPY Sample Paper KVPY Stream-SX Model Paper-28

  • question_answer
    The minimum value of the expression \[{{3}^{{{\sin }^{6}}x}}+{{3}^{{{\cos }^{6}}x}}\] is

    A) \[{{2.3}^{1/8}}\]

    B) \[{{2.3}^{7/8}}\]

    C) \[{{3.2}^{1/8}}\]

    D) 6

    Correct Answer: A

    Solution :

    \[{{3}^{{{\sin }^{6}}x}}\operatorname{and}\,{{3}^{co{{s}^{6}}}}^{x}\].are positive numbers.
    And A.M >GM \[\Rightarrow \]\[\frac{{{3}^{{{\sin }^{6}}x}}+{{3}^{{{\cos }^{6}}x}}}{2}\ge \sqrt{{{3}^{{{\sin }^{6}}x+{{\cos }^{6}}}}}\]              ...(1)
    \[=2\sqrt{{{3}^{1-\frac{3}{4}{{\sin }^{2}}2x}}}\] \[\Rightarrow \]\[{{3}^{{{\sin }^{6}}x}}+{{3}^{{{\cos }^{6}}x}}\ge 2.\sqrt{{{3}^{\frac{1}{4}}}}={{2.3}^{1/8}}\]


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