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If (a_n=2n+(-1)^n), what is the value of (a_5)?
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Answer and explanation
Correct answer: 9
Putting n = 5, a_5 = 2(5) + (-1)^5 = 10 - 1 = 9. Since 5 is odd, (-1)^5 = -1. The value 11 would result from incorrectly taking (-1)^5 as +1. Exam tip: remember that (-1)^n is +1 for even n and -1 for odd n.
Frequently asked questions
What is the correct answer to this question?
9
Why is this the correct answer?
Putting n = 5, a_5 = 2(5) + (-1)^5 = 10 - 1 = 9. Since 5 is odd, (-1)^5 = -1. The value 11 would result from incorrectly taking (-1)^5 as +1. Exam tip: remember that (-1)^n is +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: nth term.
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