Which option contains the first three terms formed by (a_n=n^2+3n-1)?
Answer and explanation
Correct answer: (3, 9, 17)
Substitute \(n=1,2,3\) into the rule: \(a_1=1^2+3(1)-1=3\), \(a_2=2^2+3(2)-1=9\), and \(a_3=3^2+3(3)-1=17\). Thus, the first three terms are \((3, 9, 17)\), so option B is correct. In option A, the second term is 9, but the first and third terms do not follow the rule. Exam tip: for a general-term question, begin by substituting \(n=1\).
Frequently asked questions
What is the correct answer to this question?
(3, 9, 17)
Why is this the correct answer?
Substitute \(n=1,2,3\) into the rule: \(a_1=1^2+3(1)-1=3\), \(a_2=2^2+3(2)-1=9\), and \(a_3=3^2+3(3)-1=17\). Thus, the first three terms are \((3, 9, 17)\), so option B is correct. In option A, the second term is 9, but the first and third terms do not follow the rule. Exam tip: for a general-term question, begin by substituting \(n=1\).
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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