JEE Main & Advanced Mathematics Trigonometric Equations Question Bank Critical Thinking

  • question_answer
    If \[\sin 2x+\sin 4x=2\sin 3x,\]then \[x\]= [EAMCET 1989]

    A) \[\frac{n\pi }{3}\]

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

    C) \[2n\pi \pm \frac{\pi }{3}\]

    D) None of these

    Correct Answer: A

    Solution :

    \[2\sin 3x\cos x-2\sin 3x=0\], \[\therefore \] \[\sin 3x=0\], \[\cos x=1\] \[\frac{1}{2}=\frac{\frac{3h}{120}-\frac{h}{120}}{1+\frac{3{{h}^{2}}}{14400}}\Rightarrow h=120,\,40\] \[3x=n\pi \] or \[x=\frac{n\pi }{3}\] and \[x=2n\pi \] The second value \[x=2n\pi \] is included in the value given by\[x=\frac{n\pi }{3}\].


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