KVPY Sample Paper KVPY Stream-SX Model Paper-8

  • question_answer
    \[f(x)={{(-1)}^{\left[ \frac{2x}{\pi } \right]}},\]\[g(x),\left| \,\sin x\, \right|-\left| \,\cos x\, \right|,\]\[\phi (x)=f(x)g(x),\] where [ ] denotes G.I.F. then fundamental period of \[f(x),\,\,g(x),\,\,\phi (x)\] are -

    A) \[\pi ,\pi ,\pi \]                

    B) \[\pi ,\,\,2\pi ,\,\,\pi \]

    C) \[\pi ,\,\,\pi ,\,\,\frac{\pi }{2}\]     

    D) \[\pi ,\,\,\frac{\pi }{2},\pi \]

    Correct Answer: C

    Solution :

    \[f(x+\pi )={{(-1)}^{\left[ \frac{2x}{\pi }+2 \right]}}={{(-1)}^{\frac{2x}{\pi }}}=f(x)\]
    period \[=\pi \]
    \[g\,\,(x+\pi )=g(x)\to period\,\,=\pi \]
    \[\phi \,(x)=f(x)\,\,g(x)={{(-\,1)}^{\left[ \frac{2x}{\pi } \right]}}.(|\,sinx\,|-|\,\cos x\,|)\]
    \[\phi \,\,\left( \frac{\pi }{2}+x \right)={{(-\,1)}^{\left[ \frac{2x}{\pi } \right]}}.(-\,1)[|\,\cos x\,|-|\,\cos x\,|]\]
                \[=f(x).\,g(x)\to period=\frac{\pi }{2}\]


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