If (a_n=9-2n), which is the first term less than (-15)?
Answer and explanation
Correct answer: 13th term
The required condition is \(9-2n<-15\). This gives \(-2n<-24\), so \(n>12\). Since \(n\) must be a positive integer, the smallest value greater than 12 is 13. Therefore, the 13th term is the first term less than \(-15\). The 12th term equals \(-15\), so it is not correct. Exam tip: for “less than,” retain the strict inequality \(<\).
Frequently asked questions
What is the correct answer to this question?
13th term
Why is this the correct answer?
The required condition is \(9-2n<-15\). This gives \(-2n<-24\), so \(n>12\). Since \(n\) must be a positive integer, the smallest value greater than 12 is 13. Therefore, the 13th term is the first term less than \(-15\). The 12th term equals \(-15\), so it is not correct. Exam tip: for “less than,” retain the strict inequality \(<\).
Which subject and chapter does this question cover?
This is a Class 9 Mathematics question. Chapter: Sequences and Progressions. Topic: nth term.
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