If (a_n=5n^2-1), which term is (124)?
Answer and explanation
Correct answer: fifth term
For 124, set \(5n^2-1=124\). Then \(5n^2=125\), so \(n^2=25\) and \(n=5\). Since a term number must be a positive integer, 124 is the fifth term. Although \(n=-5\) can arise algebraically from squaring, it cannot be a term number. Exam tip: To find the position of a given term, equate \(a_n\) to that value and solve for \(n\).
Frequently asked questions
What is the correct answer to this question?
fifth term
Why is this the correct answer?
For 124, set \(5n^2-1=124\). Then \(5n^2=125\), so \(n^2=25\) and \(n=5\). Since a term number must be a positive integer, 124 is the fifth term. Although \(n=-5\) can arise algebraically from squaring, it cannot be a term number. Exam tip: To find the position of a given term, equate \(a_n\) to that value and solve for \(n\).
Which subject and chapter does this question cover?
This is a Class 9 Mathematics question. Chapter: Sequences and Progressions. Topic: nth term.
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