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Trigonometry - Definitions (CIE A Level Maths: Pure 1)
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°
Worked example
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