If (a=13) and (d=-3), what is the value of (a_9)?
Answer and explanation
Correct answer: -11
The formula for the nth term of an arithmetic progression is \(a_n=a+(n-1)d\). Thus, \(a_9=13+(9-1)(-3)=13-24=-11\). Therefore, \(-11\) is correct. \(-9\) can result from using an incorrect number of common differences. Exam tip: when \(d\) is negative, check the sign after multiplication carefully.
Frequently asked questions
What is the correct answer to this question?
-11
Why is this the correct answer?
The formula for the nth term of an arithmetic progression is \(a_n=a+(n-1)d\). Thus, \(a_9=13+(9-1)(-3)=13-24=-11\). Therefore, \(-11\) is correct. \(-9\) can result from using an incorrect number of common differences. Exam tip: when \(d\) is negative, check the sign after multiplication carefully.
Which subject and chapter does this question cover?
This is a Class 9 Mathematics question. Chapter: Sequences and Progressions. Topic: Arithmetic Progression.
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