If \(a_n=\frac{n(4n+1)}{2}\), what is the value of \(a_5\)?
Answer and explanation
Correct answer: \(\frac{105}{2}\)
Substitute \(n=5\): \(a_5=\frac{5(4\times5+1)}{2}=\frac{5(21)}{2}=\frac{105}{2}\). Hence, option C is correct. \(\frac{101}{2}\) may result from evaluating \(4\times5+1\) incorrectly. Exam tip: after substituting the term number in a general term, follow the order of operations carefully.
Frequently asked questions
What is the correct answer to this question?
\(\frac{105}{2}\)
Why is this the correct answer?
Substitute \(n=5\): \(a_5=\frac{5(4\times5+1)}{2}=\frac{5(21)}{2}=\frac{105}{2}\). Hence, option C is correct. \(\frac{101}{2}\) may result from evaluating \(4\times5+1\) incorrectly. Exam tip: after substituting the term number in a general term, follow the order of operations 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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