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

  • question_answer
    If arithmetic mean of two positive numbers is \[A\], their geometric mean is \[G\] and harmonic mean is \[H\], then \[H\]is equal to [MP PET 2004]

    A) \[1.2+2.3+3.4+4.5+.........\]

    B) \[\frac{G}{{{A}^{2}}}\]

    C) \[\frac{{{A}^{2}}}{G}\]

    D) \[\frac{A}{{{G}^{2}}}\]

    Correct Answer: A

    Solution :

    Let the positive number \[{{a}_{1}}\] and \[{{a}_{2}}\] \[{{a}_{1}},\,A,\,{{a}_{2}}\]????A.P. then \[A=\frac{{{a}_{1}}+{{a}_{2}}}{2}\] \[{{G}^{2}}=AH\] ????.G.P. \[G=\sqrt{{{a}_{1}}{{a}_{2}}}\] \[\frac{1}{{{a}_{1}}},\,\frac{1}{H},\,\frac{1}{{{a}_{2}}}\]??..H.P. \[\frac{2}{H}=\frac{1}{{{a}_{1}}}+\frac{1}{{{a}_{2}}}\]; \[H=\frac{2{{a}_{1}}{{a}_{2}}}{{{a}_{1}}+{{a}_{2}}}\]; \[H=\frac{{{G}^{2}}}{A}\]


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