If \(a_n=\frac{n(3n+5)}{2}\), what is the value of \(a_8\)?
Answer and explanation
Correct answer: 116
Using \(a_n=\frac{n(3n+5)}{2}\), substitute \(n=8\): \(a_8=\frac{8(3\times8+5)}{2}=\frac{8(29)}{2}=4\times29=116\). Hence, option C is correct. A value such as \(112\) can result from an error while evaluating the expression inside the bracket. Exam tip: substitute the value of \(n\) first, then simplify brackets and multiplication/division step by step.
Frequently asked questions
What is the correct answer to this question?
116
Why is this the correct answer?
Using \(a_n=\frac{n(3n+5)}{2}\), substitute \(n=8\): \(a_8=\frac{8(3\times8+5)}{2}=\frac{8(29)}{2}=4\times29=116\). Hence, option C is correct. A value such as \(112\) can result from an error while evaluating the expression inside the bracket. Exam tip: substitute the value of \(n\) first, then simplify brackets and multiplication/division step by step.
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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