JEE Main & Advanced Mathematics Sequence & Series Question Bank Relation between AP., GP. and HP.

  • question_answer
    If \[\frac{x+y}{2},\ y,\ \frac{y+z}{2}\] are in H.P., then \[x,\ y,\ z\]are in  [RPET 1989; MP PET 2003]

    A) A.P.

    B) G.P.

    C) H.P.

    D) None of these

    Correct Answer: B

    Solution :

    If \[\frac{x+y}{2},\ y,\ \frac{y+z}{2}\] are in H.P., then \[=\frac{1}{2}{{x}_{1}}{{y}_{1}}\left| \ \begin{matrix}    1 & 1 & 1  \\    r & r & 1  \\    {{r}^{2}} & {{r}^{2}} & 1  \\ \end{matrix}\  \right|=0\] \[y=\frac{xy+xz+{{y}^{2}}+yz}{x+2y+z}\] \[\Rightarrow \] \[xy+2{{y}^{2}}+yz=xy+xz+{{y}^{2}}+yz\]\[\Rightarrow \]\[{{y}^{2}}=xz\] Thus \[x,\ y,\ z\] will be in G.P.


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