KVPY Sample Paper KVPY Stream-SX Model Paper-15

  • question_answer
    The number of roots of the equation, \[\sin \,x+2\sin 2x=3+\sin \,\,3x\] is-

    A) 0

    B) 1             

    C)  2

    D) infinite       

    Correct Answer: A

    Solution :

    \[(\sin x-sin3x)+2sin2x=3\]
    \[\Rightarrow -\,2\sin x\,\cos 2x+2\,\,\sin 2x=3\]
    \[\Rightarrow 2\sin x\cos 2x-2\sin 2x+3=0\]
    \[2\sin x\cos 2x-2\sin \,\,2x+({{\sin }^{2}}x+{{\cos }^{2}}x)\]\[+\,\,({{\sin }^{2}}2x+{{\cos }^{2}}2x)+1=0\]
    \[\Rightarrow {{(1-\sin 2x)}^{2}}+{{(\sin x+\cos \,2x)}^{2}}+{{\cos }^{2}}x=0\]
    \[\Rightarrow \]No root


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