JEE Main & Advanced Mathematics Trigonometric Identities Question Bank Self Evaluation Test - Trigonometric Function

  • question_answer
    For which real values of x and y, the equation \[{{\sec }^{2}}\theta =\frac{4xy}{{{(x+y)}^{2}}}\]is possible ?

    A) \[x=y\]             

    B) \[x>y\]

    C) \[x<y\]             

    D)  None of these

    Correct Answer: A

    Solution :

    Given equation, \[{{\sec }^{2}}\theta =\frac{4xy}{{{(x+y)}^{2}}}\] Since range of \[\sec \theta \] is  \[(-\infty ,-1]\,\cup [1,\infty ).\] \[\therefore \,\,{{\sec }^{2}}\theta \ge 1\]  \[\Rightarrow \,\,\frac{4xy}{{{(x+y)}^{2}}}\ge 1\] \[\Rightarrow \,\,{{(x-y)}^{2}}\le 0\] But \[{{(x-y)}^{2}}</0\] for any x, \[y\in R\] \[\therefore \,\,\,{{(x-y)}^{2}}=0\Rightarrow x=y\]


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