JEE Main & Advanced Mathematics Sequence & Series Question Bank nth term of special series, Sum to n terms and Infinite number of terms

  • question_answer
    If \[{{t}_{n}}=\frac{1}{4}(n+2)\,(n+3)\] for n = 1, 2, 3,?? then \[\frac{1}{{{t}_{1}}}+\frac{1}{{{t}_{2}}}+\frac{1}{{{t}_{3}}}+....+\frac{1}{{{t}_{2003}}}=\] [EAMCET 2003]

    A) \[\frac{4006}{3006}\]

    B) \[\frac{4003}{3007}\]

    C) \[\frac{4006}{3008}\]

    D) \[\frac{4006}{3009}\]

    Correct Answer: D

    Solution :

    \[{{t}_{n}}=\frac{1}{4}(n+2)(n+3)\], then \[\frac{1}{{{t}_{1}}}+\frac{1}{{{t}_{2}}}+\frac{1}{{{t}_{3}}}+.....+\frac{1}{{{t}_{2003}}}\]     \[=4\left[ \frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+....+\frac{1}{(2005).(2006)} \right]\]     \[=4\left[ \frac{1}{3}-\frac{1}{2006} \right]\]\[=4.\frac{2003\,}{3(2006)}=\frac{4006}{3009}\].


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