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

  • question_answer
    If \[\tan \theta =\frac{-4}{3},\]then\[\sin \theta =\] [IIT 1979; Pb. CET 1995; Orissa JEE 2002]

    A) - 4/5 but not 4/5

    B) - 4/5 or 4/5

    C) 4/5 but not - 4/5

    D) None of these

    Correct Answer: B

    Solution :

    Since \[\text{cose}{{\text{c}}^{2}}\theta =1+{{\cot }^{2}}\theta =1+\frac{9}{16}=\frac{25}{16}\]   \[\left( \because \tan \theta =-\frac{4}{3} \right)\] \[{{\sin }^{2}}\theta =\frac{1}{\text{cose}{{\text{c}}^{2}}\theta }=\frac{16}{25}\Rightarrow \sin \theta =\pm \frac{4}{5},\] Both the values are acceptable, since \[\tan \theta =-\frac{4}{3}\,\,\] \[\,i.e.,\theta \] lies in \[{{2}^{nd}}\]or \[{{4}^{th}}\]quadrant.


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