10th Class Mathematics Introduction to Trigonometry Question Bank MCQs - Introduction to Trigonometry

  • question_answer
    If \[\sin A+{{\sin }^{2}}A=1,\]then the value of the expression \[({{\cos }^{2}}A+{{\cos }^{4}}A)\] is (NCERT EXEMPLAR; CBSE 2020)

    A) \[1\]

    B) \[\frac{1}{2}\]

    C) \[2\]

    D) \[3\]

    Correct Answer: A

    Solution :

    [a] Given, \[\sin A+{{\sin }^{2}}A=1\]
    \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,\sin A=1-{{\sin }^{2}}A={{\cos }^{2}}A\]  \[[{{\cos }^{2}}A+{{\sin }^{2}}A=1]\]
    On squaring both sides, we get
    \[{{\sin }^{2}}A={{\cos }^{4}}A\]
    \[\Rightarrow \,\,\,\,\,\,1-{{\cos }^{2}}A={{\cos }^{4}}A\,\,\,\,\,\,\Rightarrow \,\,\,\,\,{{\cos }^{2}}A+{{\cos }^{4}}A=1\]


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