Edexcel IGCSE Maths

Revision Notes

3.7.1 Perpendicular Lines

What are perpendicular lines?

  • You should already know that PARALLEL lines have equal gradients
  • PERPENDICULAR LINES do meet each other and where they do the two lines form a right angle – ie they meet at 90°

What’s the deal with perpendicular gradients (and lines)?

  • Before you start trying to work with perpendicular gradients and lines, make sure you understand how to find the equation of a straight line – that will help you do the sorts of questions you will meet
  • Gradients m1 and m2 are PERPENDICULAR if m1 × m2 = -1
  • We can use m2 = -1 ÷ m2 to find a perpendicular gradient
    (This is called the NEGATIVE RECIPROCAL)
    If in doubt, SKETCH IT!

Worked Example

Perpendicular Lines Worked Example 1, downloadable IGCSE & GCSE Maths revision notes

Sketch-Perpendicular-Lines, downloadable IGCSE & GCSE Maths revision notes

Perpendicular Lines Worked Example 2, downloadable IGCSE & GCSE Maths revision notes


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