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If (a_n=n^2+4n), what is the value of (a_{10}+a_1)?
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Answer and explanation
Correct answer: 145
Given \(a_n=n^2+4n\), \(a_{10}=10^2+4(10)=100+40=140\) and \(a_1=1^2+4(1)=1+4=5\). Therefore, \(a_{10}+a_1=140+5=145\). Note that \(140\) is only \(a_{10}\), not the required sum. Exam tip: substitute each value of \(n\) into the formula separately before adding the terms.
Frequently asked questions
What is the correct answer to this question?
145
Why is this the correct answer?
Given \(a_n=n^2+4n\), \(a_{10}=10^2+4(10)=100+40=140\) and \(a_1=1^2+4(1)=1+4=5\). Therefore, \(a_{10}+a_1=140+5=145\). Note that \(140\) is only \(a_{10}\), not the required sum. Exam tip: substitute each value of \(n\) into the formula separately before adding the terms.
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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