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Trig Identity

Age 16 to 18
Challenge Level



In this diagram $O$ is the centre of a unit circle (i.e. a circle with radius 1).

Use it to find two trigonometrical relationships between $A$ and $2A$.



Did you know ... ?

Trigonometrical expressions can often be derived algebraically or geometrically. In more advanced applications the functions of trigonometry are defined as infinite power series rather than geometric ratios.