ABSTRACT
Trigonometry deals with the relationships between the sides and the angles of a triangle. Provided that a minimum of 3 sides; 2 sides and 1 angle; or 1 side and 2 angles, are known about any triangle, the other unknown sides or angles can be calculated using trigonometrical methods. Trigonometry is based on the trigonometrical ratios of sine, cosine and tangent, which are the ratios between the sides of a right-angled triangle. The values of these ratios depend upon the size of the angles, and do not depend on the size of the triangle. This chapter describes the Pythagoras theorem for finding the third side of a right-angled triangle when the other two sides are known. It discusses the sine and cosine rules to calculate sides and angles in triangles without a right angle. The compound angle formulae can be used to obtain expressions for the sum or difference of sines or cosines.
