Revision Notes

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. 

  1. Gradients m1 and m2 are PERPENDICULAR if m1 × m2 = -1
  2. We can use m2 = -1 ÷ m2 to find a perpendicular gradient
    (This is called the NEGATIVE RECIPROCAL

If in doubt, SKETCH IT

Example

Perpendicular Lines Example 1, IGCSE & GCSE Maths revision notes

Sketch Perpendicular Lines, IGCSE & GCSE Maths revision notes

Perpendicular Lines Example 2, IGCSE & GCSE Maths revision notes

Question

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Edexcel GCSE Maths Notes

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