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Class 9MathematicsSequences and ProgressionsExplicit or general ruleEasyLevel 51
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If (a_n=n^2+2n), what is the value of (a_4)?

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Answer and explanation

Correct answer: 24

Substitute n=4: a_4=4^2+2(4)=16+8=24. Therefore, 24 is the correct answer. The value 20 results from incorrectly using n instead of 2n in the second term. Exam tip: when finding a term, substitute the term number into every part of the expression.

Related tags

SequencesProgressionsExplicit RuleNth TermAlgebraic SubstitutionClass 9

Frequently asked questions

What is the correct answer to this question?

24

Why is this the correct answer?

Substitute n=4: a_4=4^2+2(4)=16+8=24. Therefore, 24 is the correct answer. The value 20 results from incorrectly using n instead of 2n in the second term. Exam tip: when finding a term, substitute the term number into every part of the expression.

Which subject and chapter does this question cover?

This is a Class 9 Mathematics question. Chapter: Sequences and Progressions. Topic: Explicit or general rule.

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10 more MCQs
  1. 1For the sequence 2, 5, 10, 17, 26, ..., the nth term is a_n = n² + 1. What is the value of a_12 − a_10?
  2. 2For the sequence 6, 14, 26, 42, ..., a_n = 2n² + 2n + 2. What is the value of a_15 - a_13?
  3. 3If a_n = (-1)^n(n + 1), what will be the value of a_7 + a_8?
  4. 4What will be the next term in the sequence (1, 2, 6, 24, 120, …)?
  5. 5If a_n = 5n + (−1)^n, what will be the value of a_10 − a_9?
  6. 6If a_n = 4n^2 + 2n - 3, what will be the value of a_11?
  7. 7If a_n = (-1)^(n+1)(2n+3), what will be the value of a_8 + a_9?
  8. 8If a_n = n^2 + 6n + 5, which term is 252?
  9. 9What is the general term of the sequence (3, 6, 9, 12, …)?
  10. 10Which explicit rule is correct for the sequence (5, 10, 15, 20, …)?
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