Plane Trigonometry

Plane Trigonometry

Trigonometry is the study of relationships between the sides and angles of a triangle. In the following figure, each angle is labelled with a capital letter and the corresponding sides with a lower case letter. As it revolves, it can be imagined that a right angled triangle ABC is formed with the right angle at C. The arm across the right angle is referred as hypotenuse.

The three basic trigonometric functions that involve the angle θ and the triangle sides are sine (sin), cosine (cos) and tangent (tan). The ratios comparing two triangle sides are given below.


Apart from using a calculator, trigonometric table is also used to find out the degree values. A part of the table is shown below.



        Find BC for the following right angled triangle.


        Answer = 17.5cm