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If (a_n=n^2+2n+5), what is the value of (a_9-a_1)?
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Answer and explanation
Correct answer: 96
Given \(a_n=n^2+2n+5\), \(a_9=9^2+2(9)+5=81+18+5=104\), while \(a_1=1^2+2(1)+5=8\). Hence, \(a_9-a_1=104-8=96\). The option 98 can result from an error while evaluating \(a_1\). Exam tip: substitute the value of \(n\) separately in each term before taking their difference.
Frequently asked questions
What is the correct answer to this question?
96
Why is this the correct answer?
Given \(a_n=n^2+2n+5\), \(a_9=9^2+2(9)+5=81+18+5=104\), while \(a_1=1^2+2(1)+5=8\). Hence, \(a_9-a_1=104-8=96\). The option 98 can result from an error while evaluating \(a_1\). Exam tip: substitute the value of \(n\) separately in each term before taking their difference.
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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