### Introduction

We originally introduced trigonometry using right-angled triangles. However, the subject has applications in dealing with any triangles such as those that might arise in surveying, navigation or the study of mechanisms.

In this Section we show how, given certain information about a triangle, we can use appropriate rules, called the Sine rule and the Cosine rule , to fully ‘solve the triangle’ i.e. obtain the lengths of all the sides and the size of all the angles of that triangle.

#### Prerequisites

• have a knowledge of the basics of trigonometry
• be aware of the standard trigonometric identities

#### Learning Outcomes

• use trigonometry in everyday situations
• fully determine all the sides and angles and the area of any triangle from partial information