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NDA 2019
Exam
NDA
Year
2019
Subject
Mathematics
Chapter
Sequences and Series

NDA 2019 · Mathematics · Sequences and Series

If the sum of first n terms of a series is (n+12) , then what is...

If the sum of first nn terms of a series is (n+12)(n+12), then what is its third term?

Options

  1. A1
  2. B2
  3. C3
  4. D4

Correct answer

A. 1

Step-by-step solution

 Given: Sn=n+12∵Tn=Sn−Sn−1∴T3=S3−S2⇒T3=(3+12)−(2+12)⇒T3=1\begin{array}{ll} & \text{ Given: } S_n=n+12 \\ \because & T_n=S_n-S_{n-1} \\ \therefore & T_3=S_3-S_2 \\ \Rightarrow & T_3=(3+12)-(2+12) \\ \Rightarrow & T_3=1\end{array}
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