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0606/23 Oct/Nov 2025, Question 9: Turning Curves into Straight Lines

Cambridge IGCSE Additional Mathematics 0606 · Paper 23 (Calculator) · Calculator · 6 marks

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The question, in short

Given paired x and y values for a relationship y = Ax^b, plot ln y versus ln x on the provided axes and then determine the constants A and b from the line.

Summarised in our own words. Use the official paper for the exact wording and any diagrams.

Part (a) · 2 marks

Using the table of x and y values, plot ln y against ln x on the given grid to produce a straight line.

  1. 1ln x: −0.5, 1.5, 2.5, 3.5
  2. 2ln y: 0.5, 1.5, 2, 2.5
  3. 3Plot the four points and draw a single ruled straight line through them

AnswerPoints (−0.5, 0.5), (1.5, 1.5), (2.5, 2), (3.5, 2.5) plotted with a single ruled straight line of best fit

Part (b) · 4 marks

From your plotted line, work out the numerical values of the constants A and b.

  1. 1ln y = b ln x + ln A
  2. 2Gradient b = (2.5 − 0.5)/(3.5 − (−0.5)) = 0.5
  3. 3Intercept: 2.5 = 0.5 × 3.5 + ln A, so ln A = 0.75
  4. 4A = e^0.75 ≈ 2.12

Answerb = 0.48 to 0.52, A = 2.01 to 2.23

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