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4MA1/1HR Jan 2023, Question 23: Equation of the Tangent Line

Pearson Edexcel International GCSE Mathematics A 4MA1 · Paper 1HR (Higher) · Calculator · 5 marks

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The question, in short

Find the equation of line Q through point G on y = 8x² − 14x − 6 where the gradient is 10, with Q perpendicular to the tangent at G, in the form ax + by + c = 0.

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Solution · 5 marks

  1. 1dy/dx = 16x − 14 = 10, so x = 1.5
  2. 2y = 8 × 1.5² − 14 × 1.5 − 6 = −9, so G is (1.5, −9)
  3. 3Q is perpendicular to gradient 10, so its gradient is −1/10
  4. 4y + 9 = −1/10 (x − 1.5), so 10y + 90 = −x + 1.5
  5. 5Multiply by 2 and rearrange: 2x + 20y + 177 = 0

Answer2x + 20y + 177 = 0

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