To solve problems involving non-right-angled triangles, the correct rule must first be chosen.
The cosine rule can be used in any triangle to calculate:
The sine rule can be used in any triangle to calculate:
Ship A leaves port P and travels on a bearing of 200°. A second ship B leaves the same port P at the same time and travels on a bearing of 165°. After half an hour ship A has travelled 5.2 km and ship B has travelled 5.8 km. How far apart are the ships after half an hour? Give the answer to three significant figures.
Remember a bearing is an angle measured clockwise from north. The angle APB = .
Two sides and the angle in between are known. Calculate the length AB.
Use the cosine rule.
AB = 3.36 km