JEE Main & Advanced Mathematics Sequence & Series Question Bank Geometric Progression

  • question_answer
    If \[{{a}^{2}}+a{{b}^{2}}+16{{c}^{2}}=2(3ab+6bc+4ac)\], where \[a,b,c\] are non-zero numbers. Then \[a,b,c\]are in [AMU 2005]

    A)  A.P

    B) G.P

    C) H.P

    D)   None of these

    Correct Answer: B

    Solution :

    \[(a+2b+2c)\]\[(a-2b+2c)={{a}^{2}}+4{{c}^{2}}\] Þ \[{{(a+2c)}^{2}}-{{(2b)}^{2}}={{a}^{2}}+4{{c}^{2}}\] Þ \[{{a}^{2}}+4ac+4{{c}^{2}}-4{{b}^{2}}={{a}^{2}}+4{{c}^{2}}\] Þ \[4ac-4{{b}^{2}}=0\]Þ \[{{b}^{2}}=ac\] Hence a, b, c are in G.P.


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