Find the (13)th term of the AP (-4,2,8,14,\ldots).
Answer and explanation
Correct answer: \(68\)
The first term is \(a=-4\), and the common difference is \(d=2-(-4)=6\). Using \(a_n=a+(n-1)d\), we get \(a_{13}=-4+(13-1)\times6=-4+72=68\). Therefore, \(68\) is correct. \(66\) may result from incorrectly using \(11\) in place of \(n-1\). Exam tip: always use \((n-1)d\), not \(nd\), in the nth-term formula.
Frequently asked questions
What is the correct answer to this question?
\(68\)
Why is this the correct answer?
The first term is \(a=-4\), and the common difference is \(d=2-(-4)=6\). Using \(a_n=a+(n-1)d\), we get \(a_{13}=-4+(13-1)\times6=-4+72=68\). Therefore, \(68\) is correct. \(66\) may result from incorrectly using \(11\) in place of \(n-1\). Exam tip: always use \((n-1)d\), not \(nd\), in the nth-term formula.
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Arithmetic Progressions (AP). Topic: Finding the $n$th term of an AP.
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