JEE Main & Advanced Mathematics Trigonometric Equations Question Bank Solution of trigonometrical equations

  • question_answer
    If \[\sqrt{3}\cos \,\theta +\sin \theta =\sqrt{2},\]then the most general value of \[\theta \] is                        [MP PET 1991, 2002;  UPSEAT 1999]

    A) \[n\pi +{{(-1)}^{n}}\frac{\pi }{4}\]

    B) \[{{(-1)}^{n}}\frac{\pi }{4}-\frac{\pi }{3}\]

    C) \[n\pi +\frac{\pi }{4}-\frac{\pi }{3}\]

    D) \[n\pi +{{(-1)}^{n}}\frac{\pi }{4}-\frac{\pi }{3}\]

    Correct Answer: D

    Solution :

    \[\frac{\sqrt{3}}{2}\cos \theta +\frac{1}{2}\sin \theta =\frac{\sqrt{2}}{2}\]{dividing by \[\sqrt{{{(\sqrt{3})}^{2}}+{{1}^{2}}}=2\}\] \[\Rightarrow \] \[\sin \left( \theta +\frac{\pi }{3} \right)=\frac{1}{\sqrt{2}}=\sin \left( \frac{\pi }{4} \right)\] \[\Rightarrow \] \[\theta =n\pi +{{(-1)}^{n}}\frac{\pi }{4}-\frac{\pi }{3}\].


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