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Unit circle

The unit circle is the circle with radius 1, whose center is at the origin (0, 0). You can express this circle with the equation

x² + y² = 1

 

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Explanation

For the point P (x, y) on this circle it holds that x = cos θ and y = sin θ, so

cos²θ + sin²θ = 1

what you can see in the figure

This is the fundamental formula of trigonometry.

 

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