If (a_n=n^2+7n-8), what is the value of (a_9-a_4)?
Answer and explanation
Correct answer: 100
Given \(a_n=n^2+7n-8\), \(a_9=9^2+7(9)-8=81+63-8=136\) and \(a_4=4^2+7(4)-8=16+28-8=36\). Hence, \(a_9-a_4=136-36=100\). A value such as 104 can result from substituting an incorrect value for one of the terms. Exam tip: calculate each required term separately before finding their difference.
Frequently asked questions
What is the correct answer to this question?
100
Why is this the correct answer?
Given \(a_n=n^2+7n-8\), \(a_9=9^2+7(9)-8=81+63-8=136\) and \(a_4=4^2+7(4)-8=16+28-8=36\). Hence, \(a_9-a_4=136-36=100\). A value such as 104 can result from substituting an incorrect value for one of the terms. Exam tip: calculate each required term separately before finding 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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