JEE Main & Advanced Mathematics Trigonometric Identities Question Bank Trigonometrical ratios of multiple and sub multiple angles

  • question_answer
    If \[\sec \theta =1\frac{1}{4}\], then \[\tan \frac{\theta }{2}=\]

    A) \[\frac{1}{3}\]

    B) \[\frac{3}{4}\]

    C) \[\frac{1}{4}\]

    D) \[\frac{5}{4}\]

    Correct Answer: A

    Solution :

    Given that \[\sec \theta =\frac{5}{4}\] \[\sec \theta =\frac{1+{{\tan }^{2}}(\theta /2)}{1-{{\tan }^{2}}(\theta /2)}\Rightarrow \frac{5}{4}=\frac{1+{{\tan }^{2}}(\theta /2)}{1-{{\tan }^{2}}(\theta /2)}\] Þ \[5-5{{\tan }^{2}}(\theta /2)=4+4{{\tan }^{2}}(\theta /2)\] Þ \[9{{\tan }^{2}}(\theta /2)=1\,\Rightarrow \tan (\theta /2)=\frac{1}{3}\].


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