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Which is the correct rule for the sequence (3,7,13,21,\ldots)?
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Answer and explanation
Correct answer: \(a_n=n^2+n+1\)
The correct rule is \(a_n=n^2+n+1\). Substituting \(n=1,2,3,4\) gives \(3,7,13,21\), respectively. In option A, the second term is \(6\), so it does not match the sequence. In an exam, verify a rule using at least the first two or three terms.
Frequently asked questions
What is the correct answer to this question?
\(a_n=n^2+n+1\)
Why is this the correct answer?
The correct rule is \(a_n=n^2+n+1\). Substituting \(n=1,2,3,4\) gives \(3,7,13,21\), respectively. In option A, the second term is \(6\), so it does not match the sequence. In an exam, verify a rule using at least the first two or three terms.
Which subject and chapter does this question cover?
This is a Class 9 Mathematics question. Chapter: Sequences and Progressions. Topic: Explicit or general rule.
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