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Class 9MathematicsSequences and Progressionsnth termExpertLevel 58
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A sequence has (a_n=2n^3-3n). What is the value of (a_5)?

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Answer and explanation

Correct answer: 235

Given \(a_n=2n^3-3n\), substitute \(n=5\): \(a_5=2(5)^3-3(5)=2\times125-15=250-15=235\). Hence, 235 is correct. 250 is only the value of \(2(5)^3\); the term \(3\times5\) must still be subtracted. Exam tip: evaluate the power first, then multiply and subtract.

Related tags

Sequences And ProgressionsNth TermSubstitutionCubic SequenceAlgebraic Expressions

Frequently asked questions

What is the correct answer to this question?

235

Why is this the correct answer?

Given \(a_n=2n^3-3n\), substitute \(n=5\): \(a_5=2(5)^3-3(5)=2\times125-15=250-15=235\). Hence, 235 is correct. 250 is only the value of \(2(5)^3\); the term \(3\times5\) must still be subtracted. Exam tip: evaluate the power first, then multiply and subtract.

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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10 more MCQs
  1. 1In the sequence \((1,4,9,16,\ldots)\), what is the difference between the 15th term and the 14th term?
  2. 2What is the 25th term of the sequence \((-5,-1,3,7,\ldots)\)?
  3. 3If aₙ = n³ − n, what will be the value of a₇ − a₅?
  4. 4What will be the 12th term in the sequence (3, 5, 9, 15, 23, ...)?
  5. 5If a_n = n(n + 2), what will be the value of a_11 − a_8?
  6. 6If a_n = n^2 + 5n - 2, which term is equal to 148?
  7. 7The sequence (3, 8, 15, 24, …) has general term a_n = n² + 2n. Which term is 168?
  8. 8If a_n = n³ + n², what will be the value of a_6 − a_4?
  9. 9If a_n = 4n² − 1, which term is 575?
  10. 10If a_n = n(n + 3), which term is 130?
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