The use of trigonometry is not just limited to mathematics. It is also used in physics, land surveying, engineering, satellite navigation and other applications.

Consider a right-angled triangle CAB, shown in Figure 13.1. Angle CBA (B) is a right angle, i.e. 90°. If A is being considered,

side BC is called the ‘opposite side’ or opposite. Side AC, which is the longest side, is called the ‘hypotenuse’. The third side, AB, is called the ‘adjacent side’or adjacent and is common to A as well as the right angle.