The law of cosines (also known as the cosine rule ) gives the relationship between the side lengths of a triangle and the cosine of any of its angles. It says — Learn how to use the cosine rule to find missing sides and angles in non right-angled triangles. See the formula, examples, worksheets and tips for GCSE Maths exam questions. Learn how to use the cosine rule to find the third side or the angles of a triangle when you know two sides and the angle between them. See examples, formulas, and tips to remember the law of cosines. 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. Similarly, if two sides and the angle between them is known, the cosine rule allows …
