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## Why does the Unit Circle work?

 Quote by willem2 I think the sine was defined as the opposite side divided by the hypotenuse, in a right angled triangle. I'm pretty sure sin and cos were used before cartetsian coordinates. Since the hypotenuse will be the radius of the unit circle, this has to be 1 to make the length of the side opposite to angle A equal to sin(A)
very sensible,,,
Thanks for the explanation,,,