Definitions of Trigonometric Functions (Edexcel International AS Maths) : Revision Note

Trigonometry - Definitions

What is trigonometry?

• Trigonometry looks at the relationship between side lengths and angles of triangles

• It comes from the Greek words trigonon meaning ‘triangle’ and metron meaning ‘measure’

• The three trigonometric functions Sine, Cosine and Tangent come from ratios of side lengths in right angled triangles

What is the unit circle and how does it help with trigonometry?

• The unit circle is a circle with radius 1 and centre (0, 0)

• It can be used to calculate trig values as a co‑ordinate point (x, y) on the circle

• (x, y) = (cos θ, sin θ), where θ is the angle measured anticlockwise from the positive x‑axis

• It allows us to calculate sin, cos and tan for angles greater than 90°