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JEE Advanced 2007Paper 1
Exam
JEE Advanced
Year
2007
Paper
Paper 1
Subject
Mathematics
Chapter
Sequences and Series

JEE Advanced 2007 · Paper 1 · Mathematics · Sequences and Series

Paragraph: Let V_r denotes the sum of the first r terms of an...

Paragraph: Let VrV_r denotes the sum of the first rr terms of an arithmetic progression (AP)(A P) whose first term is rr and the common difference is (2r−1)(2 r-1). Let Tr=Vr+1−Vr−2T_r=V_{r+1}-V_r-2 and Qr=Tr+1−TrQ_r=T_{r+1}-T_r for r=1,2,…r=1,2, \ldotsQuestion: Which one of the following is a correct statement?

Options

  1. AQ1,Q2,Q3,…Q_1, Q_2, Q_3, \ldots are in AP with common difference 5
  2. BQ1,Q2,Q3,…Q_1, Q_2, Q_3, \ldots are in AP with common difference 6
  3. CQ1,Q2,Q3,…Q_1, Q_2, Q_3, \ldots are in AP with common difference 11
  4. DQ1=Q2=Q3=…Q_1=Q_2=Q_3=\ldots

Correct answer

B. Q1,Q2,Q3,…Q_1, Q_2, Q_3, \ldots are in AP with common difference 6

Step-by-step solution

Since, Tr=3r2+2r−1T_r=3 r^2+2 r-1 ∴Tr+1=3(r+1)2+2(r+1)−1∴Qr=Tr+1−Tr=3[2r+1]+2[1]⇒Qr=6r+5⇒Qr+1=6(r+1)+5\begin{array}{rlrl} & \therefore & T_{r+1} & =3(r+1)^2+2(r+1)-1 \\ & \therefore & Q_r & =T_{r+1}-T_r=3[2 r+1]+2[1] \\ \Rightarrow & Q_r & =6 r+5 \\ \Rightarrow & Q_{r+1} & =6(r+1)+5 \end{array} Common difference =Qr+1−Qr=6=Q_{r+1}-Q_r=6
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