1. The unit circle is a circle with radius 1 centered at the origin (0,0) on the coordinate plane. 2. The coordinates of any point on the unit circle can be described using an angle $\theta$ measured from the positive x-axis. 3. The cosine of the angle $\theta$ is the x-coordinate of the point on the unit circle, so: $$\cos(\theta) = x$$ 4. The sine of the angle $\theta$ is the y-coordinate of the point on the unit circle, so: $$\sin(\theta) = y$$ 5. The tangent of the angle $\theta$ is defined as the ratio of sine to cosine: $$\tan(\theta) = \frac{\sin(\theta)}{\cos(\theta)} = \frac{y}{x}$$ 6. To summarize, for any angle $\theta$ on the unit circle, the trigonometric ratios are: $$\cos(\theta) = x$$ $$\sin(\theta) = y$$ $$\tan(\theta) = \frac{y}{x}$$ This is the fundamental definition of the trigonometric ratios based on the unit circle.