Which is the correct rule for the sequence (9,20,33,48,\ldots)?
Answer and explanation
Correct answer: \(a_n=n^2+8n\)
In option A, substituting \(n=1,2,3,4\) gives \(9,20,33,48\), respectively. Therefore, the correct rule is \(a_n=n^2+8n\). Option B gives the first term as 9, but for \(n=2\) it gives 19, not 20. Exam tip: Test a proposed rule by substituting values of \(n\) for at least the first three terms.
Frequently asked questions
What is the correct answer to this question?
\(a_n=n^2+8n\)
Why is this the correct answer?
In option A, substituting \(n=1,2,3,4\) gives \(9,20,33,48\), respectively. Therefore, the correct rule is \(a_n=n^2+8n\). Option B gives the first term as 9, but for \(n=2\) it gives 19, not 20. Exam tip: Test a proposed rule by substituting values of \(n\) for at least the first 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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