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NDA 2022
Exam
NDA
Year
2022
Subject
Mathematics
Chapter
Mathematical Induction

NDA 2022 · Mathematics · Mathematical Induction

Consider the following statements : 1. 2+4+6+ +2 n=n^2+n 2. The...

Consider the following statements : 1. 2+4+6+…+2n=n2+n2.Theexpression2+4+6+\ldots+2 n=n^2+n 2. The expression n^2+n+41alwaysgivesaprimenumberforeverynaturalnumberalways gives a prime number for every natural numbernWhichoftheabovestatementsis/arecorrect?Which of the above statements is/are correct?

Options

  1. A1 only
  2. B2 only
  3. CBoth 1 and 2
  4. DNeither 1 nor 2

Correct answer

A. 1 only

Step-by-step solution

Let S=2+4+6+…+2n=2(1+2+3+…+n)=2⋅n(n+1)2=n2+n∴S=2+4+6+\ldots+2 n=2(1+2+3+\ldots+n)=2 \cdot \frac{n(n+1)}{2}=n^2+n\therefore \quad Statement 1 is true. Putting n=41n=41 in n2+n+41=412+41+41=41.(41+2)=41.43n^2+n+41=41^2+41+41=41.(41+2)=41.43 Which is not prime. So, expression not always prime for n∈N\mathrm{n} \in \mathrm{N}
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