## The cosine rule

… is a favourite exam question and deals with calculating an angle or a length in any triangle. The questions tend to be on calculator exam papers as you’ll be working with fractions, squares and the cosine of an angle.

## Top tips!

- Make sure you use the ‘inclusive angle’ ie. you’ll need two sides and the angle in the middle
- Always label accurately with capital letters for angles and small case for sides
- Don’t be tempted to plug all the information into your calculator – it’s better to calculate a little at a time

Here’s a picture of my notes that might help:

Watch videos on YouTube:

How to work with the rule – intro

How to work with the rule – exam question angle in triangle

How to work with the rule – exam question length of side

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