Table of Contents
IGCSE Mathematics: Cosine Rule
Cosine Rule
The cosine is just like the sine rule, but it’s for when you know 3 sides and want to find an angle OR when you know 2 sides + 1 angle (none are opposite each other meaning no sine rule) and need to find the remaining side.
The cosine rule to find a side is just:
And the cosine for to find an angle is just:
Remember for this one you’ve only worked out the Cosine of the angle! You still need to use cos-1() to find C!
