When to Use. The Law of Cosines is useful for finding: the third side of a triangle when we know two sides and the angle between them (like the example above) the angles of a triangle when we know all three sides (as in the following example)What is the formula for cosine law?
Cosine Rule a2 = b2 + c2 - 2bc cos ∠x b2 = a2 + c2 - 2ac cos ∠y c2 = a2 + b2 - 2ab cos ∠zWhen to use cosine rule?
The cosine rule is a formula commonly used in trigonometry to determine certain aspects of a non-right triangle when other key parts of that triangle are known or can otherwise be determined.What is the cosine rule?
The cosine rule, also known as the law of cosines, relates all 3 sides of a triangle with an angle of a triangle. It is most useful for solving for missing information in a triangle. For example, if all three sides of the triangle are known, the cosine rule allows one to find any of the angle measures.