The picture shows a point on the
unit circle. Since we know that any point on the
unit circle can be described by cosθ , sinθ. It is possible to draw the triangle that describes this point. As you can see from the picture, the lenght of one side is cosθ and the length of the other side is sinθ and, by definition, the
radius of the unit circle is 1. From these facts, the primary pythagorean identity can be shown. sin
2θ + cos
2θ = 1. This identity is just an application of the
pythagorean theorem to the
unit circle.
