JEE Main & Advanced Mathematics Trigonometric Identities Question Bank Fundamental trigonometrical ratios and functions, Trigonometrical ratio of allied angles

  • question_answer
    \[{{\sin }^{6}}\theta +{{\cos }^{6}}\theta +3{{\sin }^{2}}\theta {{\cos }^{2}}\theta =\] [MP PET 1995, 2002; DCE 2005]

    A) 0

    B) -1

    C) 1

    D) None of these

    Correct Answer: C

    Solution :

    \[{{\sin }^{6}}\theta +{{\cos }^{6}}\theta +3\,{{\sin }^{2}}\theta \,{{\cos }^{2}}\theta \] \[={{({{\sin }^{2}}\theta +{{\cos }^{2}}\theta )}^{3}}-3{{\sin }^{2}}\theta {{\cos }^{2}}\theta +3{{\sin }^{2}}\theta {{\cos }^{2}}\theta =1.\] Trick: Put \[\theta ={{0}^{o}},\] we get the value of expression equal to 1. Again put \[\theta ={{45}^{o}},\] the value remains 1, it means that the expression is independent of q and is equal to 1.


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