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

  • question_answer
    If \[2(y-a)\] is the H.M. between \[y-x\] and \[y-z\], then \[x-a,\ y-a,\ z-a\] are in

    A) A.P.

    B) G.P.

    C) H.P.

    D) None of these

    Correct Answer: B

    Solution :

    \[y-x,\ 2(y-a),\ (y-z)\] are in H.P. \[\Rightarrow \] \[\frac{1}{y-x},\ \frac{1}{2(y-a)},\ \frac{1}{y-z}\]are in A.P. \[\Rightarrow \] \[\frac{1}{2(y-a)}-\frac{1}{y-x}=\frac{1}{y-z}-\frac{1}{2(y-a)}\] \[\Rightarrow \] \[\frac{2a-y-x}{y-x}=\frac{y+z-2a}{y-z}\] \[\Rightarrow \] \[\therefore \] \[\Rightarrow \] \[\frac{x-a}{y-a}=\frac{y-a}{z-a}\] (Applying componendo and dividendo) \[\Rightarrow \] \[x-a,\ y-a,\ z-a\] are in G.P.


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