KVPY Sample Paper KVPY Stream-SX Model Paper-26

  • question_answer
    Range of \[y=\cos \left( \pi \sin \left( \frac{\pi }{2}\cos (\pi sinx) \right) \right)\], where \[x\in R\] is

    A) \[\left[ -\pi ,\pi  \right]\]

    B) \[\left[ -1,1 \right]\]

    C) \[\left[ 0,1 \right]\]

    D) \[\left[ -1,0 \right]\]

    Correct Answer: B

    Solution :

    We have, \[y=\cos \left( \pi \sin \left( \frac{\pi }{2}\cos \left( \pi \sin x \right) \right) \right)\]
    \[-1\le \sin x\le 1\]
    \[\therefore \,\,\,\,-\pi \le \sin x\le \pi \] \[\Rightarrow -1\le \cos (\pi \sin x)\le 1\] \[\Rightarrow -1\le \sin \left( \frac{\pi }{2}\cos \left( \pi \sin x \right) \right)\le 1\] \[\Rightarrow -\pi \le \pi \sin \left( \frac{\pi }{2}\cos \left( \pi \sin x \right) \right)\le \pi \]
    \[\Rightarrow -1\le \cos \left( \pi \sin \left( \frac{\pi }{2}\cos \left( \pi \sin x \right) \right) \right)\le 1\] \[\Rightarrow -1\le y\le 1\] Range of \[y\in \left[ -1,1 \right]\]


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