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

  • question_answer
    If a,b,c are in A.P., then \[{{2}^{ax+1}},{{2}^{bx+1}},\,{{2}^{cx+1}},x\ne 0\] are in  [DCE 2000; Pb. CET 2000]

    A) A.P.

    B) G.P. only when \[x>\text{0}\]

    C) G.P. if \[x<0\]

    D) G.P. for all \[x\ne 0\]

    Correct Answer: D

    Solution :

    \[\frac{{{T}_{2}}}{{{T}_{1}}}=\frac{{{T}_{3}}}{{{T}_{2}}}\] \[\Rightarrow {{2}^{(b-a)x}}={{2}^{(c-b)x}}\]\[\Rightarrow (b-a)x=(c-b)x\] Þ \[(b-a)=(c-b)\] \[\forall \,x,x\ne 0\] \[\therefore {{2}^{ax+1}},{{2}^{bx+1}},{{2}^{cx+1}}\]is a G.P., \[\forall \,\,x\ne 0.\]


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