If (a_n=4n-7), what is (a_{2n+1})?
Answer and explanation
Correct answer: \(8n-3\)
Given \(a_n=4n-7\), substitute the complete index \(2n+1\) for \(n\): \(a_{2n+1}=4(2n+1)-7=8n+4-7=8n-3\). Hence, the correct answer is \(8n-3\). The option \(8n-7\) results from incorrectly ignoring the \(+4\) produced by the \(+1\) in the index. Exam tip: always place a compound index in brackets before substituting it into a formula.
Frequently asked questions
What is the correct answer to this question?
\(8n-3\)
Why is this the correct answer?
Given \(a_n=4n-7\), substitute the complete index \(2n+1\) for \(n\): \(a_{2n+1}=4(2n+1)-7=8n+4-7=8n-3\). Hence, the correct answer is \(8n-3\). The option \(8n-7\) results from incorrectly ignoring the \(+4\) produced by the \(+1\) in the index. Exam tip: always place a compound index in brackets before substituting it into a formula.
Which subject and chapter does this question cover?
This is a Class 9 Mathematics question. Chapter: Sequences and Progressions. Topic: nth term.
Student feedback
Was this question useful?
👍 0 Helpful 👎 0 Not helpful
Yes 0% No 0%
0 responsesStudent Reviews
No published reviews yet.
