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Railways Sample Paper RRBs Assistant Loco Pilot and Technician CBT STAGE-I Sample Paper-16

  • question_answer
    The value of \[\cos 52{}^\circ +\cos 68{}^\circ +\cos 172{}^\circ \]is

    A)   0

    B)         1    

    C)  \[-1\]               

    D)  \[-\frac{1}{2}\]

    Correct Answer: A

    Solution :

    \[2\cos \frac{52{}^\circ +68{}^\circ }{2}.\cos \frac{68{}^\circ -52{}^\circ }{2}+\cos \,\,(180{}^\circ -8{}^\circ )\] \[\,\,=2\cos 60{}^\circ \cdot \cos 8{}^\circ -\cos 8{}^\circ \] \[\,\,\,=2\times \frac{1}{2}\times \cos 8{}^\circ -\cos 8{}^\circ =0\]        


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