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Class 9MathematicsSequences and ProgressionsSequencesExpertLevel 41
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If (a_n=5n-(-1)^n), what will be the value of (a_8)?

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Answer and explanation

Correct answer: 39

Given \(a_n=5n-(-1)^n\). Substituting \(n=8\), \(a_8=5\times8-(-1)^8=40-1=39\), since an even power of \((-1)\) equals \(1\). Option 41 would result from incorrectly taking \((-1)^8\) as \(-1\). Exam tip: remember that \((-1)^{\text{even}}=1\) and \((-1)^{\text{odd}}=-1\).

Related tags

SequencesNth TermAlternating SignsPowers Of Minus OneClass 9 Mathematics

Frequently asked questions

What is the correct answer to this question?

39

Why is this the correct answer?

Given \(a_n=5n-(-1)^n\). Substituting \(n=8\), \(a_8=5\times8-(-1)^8=40-1=39\), since an even power of \((-1)\) equals \(1\). Option 41 would result from incorrectly taking \((-1)^8\) as \(-1\). Exam tip: remember that \((-1)^{\text{even}}=1\) and \((-1)^{\text{odd}}=-1\).

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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  1. 1What is the next term of the sequence (2,4,6,8,\ldots)?
  2. 2What is the fifth term of the sequence (5,10,15,20,\ldots)?
  3. 3Which is the fourth term in the sequence (1,3,5,7,\ldots)?
  4. 4What will be the next term of (10,20,30,40,\ldots)?
  5. 5What is the next term of (12,11,10,9,\ldots)?
  6. 6What is the sixth term of (4,8,12,16,\ldots)?
  7. 7What is the third term in (7,14,21,28,\ldots)?
  8. 8What is the next term of (30,27,24,21,\ldots)?
  9. 9The sequence (9,18,27,36,\ldots) consists of multiples of which number?
  10. 10What will be the next term of (100,90,80,70,\ldots)?
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