If (a=120), (d=-9), and (n=13), find (a_n).
Answer and explanation
Correct answer: 12
The nth term of an AP is \(a_n=a+(n-1)d\). Thus, \(a_{13}=120+(13-1)(-9)=120-108=12\). Therefore, 12 is correct. Getting 21 is a common error caused by using the negative common difference \(-9\) with the wrong sign. Exam tip: always use \(n-1\) and keep a negative \(d\) in brackets while calculating.
Frequently asked questions
What is the correct answer to this question?
12
Why is this the correct answer?
The nth term of an AP is \(a_n=a+(n-1)d\). Thus, \(a_{13}=120+(13-1)(-9)=120-108=12\). Therefore, 12 is correct. Getting 21 is a common error caused by using the negative common difference \(-9\) with the wrong sign. Exam tip: always use \(n-1\) and keep a negative \(d\) in brackets while calculating.
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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