Fundamental identities are like the main building blocks of trigonometry. They really become clear when you look at the unit circle.

• Sine and Cosine: On the unit circle, for any angle $\theta$, the coordinates are $(\cos \theta, \sin \theta)$. This shows how these functions connect to the x- and y-values on the circle.

• Pythagorean Identity: The important identity $sin^2(\theta) + cos^2(\theta) = 1$ comes from the Pythagorean theorem. This works with the unit circle, where the radius is always 1.

By exploring these identities, you can see and understand trigonometric functions much better!