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

  • question_answer
    If \[a,\ b,\ c\]are in A.P., \[b,\ c,\ d\] are in  G.P. and \[c,\ d,\ e\]are in H.P., then \[a,\ c,\ e\] are in  [AMU 1988, 2001; MP PET 1993]

    A) No particular order

    B) A.P.

    C) G.P.

    D) H.P.

    Correct Answer: C

    Solution :

    \[a,\ b,\ c\] are in A.P. then \[2b=a+c\] .....(i) \[b,\ c,\ d\] are in G.P. then\[{{c}^{2}}=bd\] ....(ii) \[c,\ d,\ e\] are in H.P. then \[d=\frac{2ce}{c+e}\] ....(iii) From (ii), \[1,\ 2,\ 3,\ ..........=n\] \[\Rightarrow \] \[{{c}^{2}}=\frac{ace+{{c}^{2}}e}{c+e}\Rightarrow {{c}^{3}}+{{c}^{2}}e=ace+{{c}^{2}}e\] \[\Rightarrow \] \[{{c}^{3}}=ace\Rightarrow {{c}^{2}}=ae\] Hence \[a,\ c,\ e\]  will be in G.P.


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