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

  • question_answer
    If \[\sin 3\alpha =4\sin \alpha \sin (x+\alpha )\sin (x-\alpha ),\]then \[x=\]

    A) \[n\pi \pm \frac{\pi }{6}\]

    B) \[n\pi \pm \frac{\pi }{3}\]

    C) \[n\pi \pm \frac{\pi }{4}\]

    D) \[n\pi \pm \frac{\pi }{2}\]

    Correct Answer: B

    Solution :

    \[3\sin \alpha -4{{\sin }^{3}}\alpha =4\sin \alpha ({{\sin }^{2}}x-{{\sin }^{2}}\alpha )\] \[\therefore \] \[{{\sin }^{2}}x={{\left( \frac{\sqrt{3}}{2} \right)}^{2}}\] Þ \[{{\sin }^{2}}x={{\sin }^{2}}\pi /3\] Þ \[x=n\pi \pm \pi /3\].


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