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If (a_n=n^2+(-1)^n), what will be the value of (a_9)?
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Answer and explanation
Correct answer: 80
Substitute \(n=9\): \(a_9=9^2+(-1)^9\). Since 9 is odd, \((-1)^9=-1\). Therefore, \(a_9=81-1=80\), so option C is correct. Option 82 would result from incorrectly taking \((-1)^9\) as \(+1\). Exam tip: \((-1)^n\) equals \(+1\) for even \(n\) and \(-1\) for odd \(n\).
Frequently asked questions
What is the correct answer to this question?
80
Why is this the correct answer?
Substitute \(n=9\): \(a_9=9^2+(-1)^9\). Since 9 is odd, \((-1)^9=-1\). Therefore, \(a_9=81-1=80\), so option C is correct. Option 82 would result from incorrectly taking \((-1)^9\) as \(+1\). Exam tip: \((-1)^n\) equals \(+1\) for even \(n\) and \(-1\) for odd \(n\).
Which subject and chapter does this question cover?
This is a Class 9 Mathematics question. Chapter: Sequences and Progressions. Topic: Sequences.
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