If \(a_n=\frac{n(n+1)}{2}\), what is the value of \(a_4\)?
Answer and explanation
Correct answer: 10
Substitute \(n=4\): \(a_4=\frac{4(4+1)}{2}=\frac{4\times5}{2}=10\). Therefore, the correct answer is 10. Getting 12 usually results from an error in addition or multiplication. Exam tip: for a general term, substitute the given subscript for \(n\) and simplify step by step.
Frequently asked questions
What is the correct answer to this question?
10
Why is this the correct answer?
Substitute \(n=4\): \(a_4=\frac{4(4+1)}{2}=\frac{4\times5}{2}=10\). Therefore, the correct answer is 10. Getting 12 usually results from an error in addition or multiplication. Exam tip: for a general term, substitute the given subscript for \(n\) and simplify 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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