Trigonometry

In geometry the angle between two lines is measured in degrees, but in trigonometry the size of an acute angle is described by the ratio of two of the sides of a right angled triangle containing the angle. The main advantage of using trigonometrical ratios is that distances can be calculated which can not be measured directly, in astronomy, surveying, navigation and travel problems. Another advantage is that angles can be introduced into equations without any change of units because ratios are numbers, and this is important in mathematics and physics.