Which is the correct rule for the sequence (4,10,18,28,\ldots)?
Answer and explanation
Correct answer: \(a_n=n^2+3n\)
Substituting \(n=1,2,3,4\) into \(a_n=n^2+3n\) gives \(4,10,18,28\), respectively. Therefore, option A is correct. Option C gives the first two terms as \(4,10\), but its third term is \(20\), not \(18\). Exam tip: Verify a proposed sequence rule using at least three or four terms.
Frequently asked questions
What is the correct answer to this question?
\(a_n=n^2+3n\)
Why is this the correct answer?
Substituting \(n=1,2,3,4\) into \(a_n=n^2+3n\) gives \(4,10,18,28\), respectively. Therefore, option A is correct. Option C gives the first two terms as \(4,10\), but its third term is \(20\), not \(18\). Exam tip: Verify a proposed sequence rule using at least three or four 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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