If (a=19) and (d=-5), what is the value of (a_9)?
Answer and explanation
Correct answer: -21
For an arithmetic progression, the nth term is \(a_n=a+(n-1)d\). Thus, \(a_9=19+(9-1)(-5)=19-40=-21\). Therefore, option B is correct. The value \(-19\) would result from incorrectly using 7 in place of \(n-1\). Exam tip: when the common difference is negative, check the sign after multiplication carefully.
Frequently asked questions
What is the correct answer to this question?
-21
Why is this the correct answer?
For an arithmetic progression, the nth term is \(a_n=a+(n-1)d\). Thus, \(a_9=19+(9-1)(-5)=19-40=-21\). Therefore, option B is correct. The value \(-19\) would result from incorrectly using 7 in place of \(n-1\). Exam tip: when the common difference 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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