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0606/22 Feb/Mar 2025, Question 5: Turning Curves into Straight Lines

Cambridge IGCSE Additional Mathematics 0606 · Paper 22 (Calculator) · Calculator · 7 marks

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The question, in short

A graph of e^y against x² is a straight line with gradient −3 through (4.30, 5.85). Find y in terms of x, then the x values for which y exists.

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Part (a) · 4 marks

Use the gradient and the given point to form the linear relation, then take logs to express y in terms of x.

  1. 1e^y = mx² + c with m = −3
  2. 25.85 = −3(4.30) + c
  3. 3c = 18.75
  4. 4e^y = 18.75 − 3x², so y = ln(18.75 − 3x²)

Answery = ln(18.75 − 3x²)

Part (b) · 3 marks

Determine the range of x² for which the resulting y is defined, giving the allowed x values.

  1. 1y exists when 18.75 − 3x² > 0
  2. 2x² < 6.25
  3. 3Critical values ±2.5
  4. 4−2.5 < x < 2.5

Answer−2.5 < x < 2.5

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