## The Unit Circle.

### Unit Circle Definition.

 $$\sin \theta = y$$ $$\cos \theta = x$$ $$\ds\csc \theta = \frac1y$$ $$\ds\sec \theta = \frac1x$$ $$\ds\tan \theta = \frac yx$$ $$\ds\cot \theta = \frac xy$$

### Right Triangle Definition.

 $$\ds\sin \theta = \frac{\text{O} }{\text{H} }$$ $$\ds\csc \theta = \frac{\text{H} }{\text{O} }$$ $$\ds\cos \theta = \frac{\text{A} }{\text{H} }$$ $$\ds\sec \theta = \frac{\text{H} }{\text{A} }$$ $$\ds\tan \theta = \frac{\text{O} }{\text{A} }$$ $$\ds\cot \theta = \frac{\text{A} }{\text{O} }$$