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NDA 2026
Exam
NDA
Year
2026
Subject
Mathematics
Chapter
Sequences and Series

NDA 2026 · Mathematics · Sequences and Series

If p^ th term of an AP is k , then what is the sum of p^ th term,...

If pthp^{\text{th}} term of an AP is kk, then what is the sum of pthp^{\text{th}} term, (p+q)th(p+q)^{\text{th}} term and (p−q)th(p-q)^{\text{th}} term of the AP ?

Options

  1. A2k2k
  2. B3k3k
  3. C4k4k
  4. D5k5k

Correct answer

B. 3k3k

Step-by-step solution

Let the first term of the AP be aa and the common difference be dd.

The pthp^{\text{th}} term is given by Tp=a+(p−1)d=kT_p = a + (p-1)d = k.

The (p+q)th(p+q)^{\text{th}} term is Tp+q=a+(p+q−1)dT_{p+q} = a + (p+q-1)d.

The (p−q)th(p-q)^{\text{th}} term is Tp−q=a+(p−q−1)dT_{p-q} = a + (p-q-1)d.

The required sum is Tp+Tp+q+Tp−qT_p + T_{p+q} + T_{p-q}.

Substituting the values, we get:

[a+(p−1)d]+[a+(p+q−1)d]+[a+(p−q−1)d][a + (p-1)d] + [a + (p+q-1)d] + [a + (p-q-1)d]

=3a+d[(p−1)+(p+q−1)+(p−q−1)]= 3a + d[(p-1) + (p+q-1) + (p-q-1)]

=3a+d(3p−3)= 3a + d(3p - 3)

=3[a+(p−1)d]= 3[a + (p-1)d]

Since a+(p−1)d=ka + (p-1)d = k, the sum is 3k3k.

Answer: 3k3k
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