Which explicit rule is correct for the sequence (7,24,51,88,\ldots)?
Answer and explanation
Correct answer: \(a_n=5n^2+2n\)
For \(a_n=5n^2+2n\), substituting \(n=1,2,3,4\) gives \(7,24,51,88\), respectively. Hence, it is the required explicit rule. Although \(a_n=3n^2+4n\) gives the first term as 7, it gives 20, not 24, when \(n=2\). Exam tip: test a rule using at least the first three terms.
Frequently asked questions
What is the correct answer to this question?
\(a_n=5n^2+2n\)
Why is this the correct answer?
For \(a_n=5n^2+2n\), substituting \(n=1,2,3,4\) gives \(7,24,51,88\), respectively. Hence, it is the required explicit rule. Although \(a_n=3n^2+4n\) gives the first term as 7, it gives 20, not 24, when \(n=2\). Exam tip: test a rule using 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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