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0580/21 May/Jun 2021, Question 6: Quadratic and Cubic Sequences

Cambridge IGCSE Mathematics 0580 · Paper 21 (Extended) · Calculator · 4 marks

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The question, in short

Use the given nth term rule to generate the first three terms, then work out the nth term rule for a sequence starting 25, 18, 11, 4, −3.

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Part (a) · 2 marks

Substitute n = 1, 2 and 3 into n² + 3n to find the first three terms.

  1. 1n = 1: 1² + 3 × 1 = 4
  2. 2n = 2: 2² + 3 × 2 = 10
  3. 3n = 3: 3² + 3 × 3 = 18
  4. 4First three terms: 4, 10, 18

Answer4, 10, 18

Part (b) · 2 marks

Find the nth term of the sequence 25, 18, 11, 4, −3.

  1. 1The terms go down by 7, so use −7n
  2. 2Zero term = 25 + 7 = 32
  3. 3nth term = 32 − 7n

Answer32 − 7n

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Also searched as: 0580/21/M/J/21 · 0580_s21_qp_21 · 0580 s21 21 · question 6.
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