JEE Main & Advanced Mathematics Sequence & Series Question Bank Self Evaluation Test - Sequences and Series

  • question_answer
    Let \[{{a}_{n}}\] be the nth term of an A.P. If \[\sum\limits_{r=1}^{100}{{{a}_{2r}}=\alpha }\] and \[\sum\limits_{r=1}^{100}{{{a}_{2r-1}}=\beta }\], then the common difference of the A.P. is

    A) \[\alpha -\beta \]

    B) \[\beta -\alpha \]

    C) \[\frac{\alpha -\beta }{2}\]

    D) None

    Correct Answer: D

    Solution :

    [d] Let d be the common difference of the A.P. Then \[{{a}_{2r}}={{a}_{2r-1}}+d\]. \[\therefore \sum\limits_{r=1}^{100}{{{a}_{2r}}=\sum\limits_{r=1}^{100}{({{a}_{2r-1}}+d)}=\sum\limits_{r=1}^{100}{{{a}_{2r-1}}+100d}}\] \[\Rightarrow \alpha =\beta +100\,d\Rightarrow d=\frac{\alpha -\beta }{100}\]


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