If (a_n=7n^2-4n+1), what is the value of (a_5)?
Answer and explanation
Correct answer: 156
Given \(a_n=7n^2-4n+1\), substitute \(n=5\): \(a_5=7(5)^2-4(5)+1=7\times25-20+1=175-20+1=156\). Hence, 156 is correct. The value 154 may result from incorrectly omitting the final \(+1\). Exam tip: substitute the term number first, then evaluate powers and multiplication carefully.
Frequently asked questions
What is the correct answer to this question?
156
Why is this the correct answer?
Given \(a_n=7n^2-4n+1\), substitute \(n=5\): \(a_5=7(5)^2-4(5)+1=7\times25-20+1=175-20+1=156\). Hence, 156 is correct. The value 154 may result from incorrectly omitting the final \(+1\). Exam tip: substitute the term number first, then evaluate powers and multiplication carefully.
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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