KVPY Sample Paper KVPY Stream-SX Model Paper-16

  • question_answer
    If x, y, z are unequal positive numbers in H.P., then \[{{x}^{3}}+{{z}^{3}}\]

    A) \[\ge 2{{y}^{3}}\]

    B) \[\le 2{{y}^{3}}\]

    C) \[>2{{y}^{3}}~\]

    D) none of these

    Correct Answer: C

    Solution :

    \[\Rightarrow x,y,z\] are in H.P.
    \[\Rightarrow y=H.M.\] of x and z
    \[\because G.M.>H.M.\]
    \[\Rightarrow \sqrt{xz}>y\]
    Again, Since A.M. > G.M.
                (Here x, y, z are unequal)
    \[\therefore \frac{{{x}^{3}}+{{z}^{3}}}{2}>\sqrt{{{(xz)}^{3}}}>{{y}^{3}}\]
    \[\Rightarrow {{x}^{3}}+{{z}^{3}}>2{{y}^{3}}\]


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