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

  • question_answer
    Three number are in A.P. such that their sum is 18 and sum of their squares is 158. The greatest number among them is [UPSEAT 2004]

    A) 10

    B) 11

    C) 12

    D) None of these

    Correct Answer: B

    Solution :

    Let three number of A.P. \[a-d,\,a,\,\]\[a+d\] Sum = 18, and \[{{(a-d)}^{2}}+{{a}^{2}}+{{(a+d)}^{2}}=58\] \[a-d+a+a+d=18\] \[a=6\] and \[{{(6-d)}^{2}}+36+{{(6+d)}^{2}}=158\] = \[36+{{d}^{2}}+36+{{d}^{2}}=122\]\[=2{{d}^{2}}+72=122\] \[=2{{d}^{2}}=50\] Þ \[d=5\]. Hence Numbers are 1, 6, 11, i.e. maximum number is 11.


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