The radius over here, the distance from the center of the circle which is at the origin to any point in the circle or any point on the circle, I should say, this radius is equal to one.
This is the point negative one comma zero and this is the point zero comma negative one. For example this point right over here is the point one comma zero. Right over here I've draw a unit circle, and when we say a unit circle we're talking about a circle with radius one. Voiceover: Let's review the unit circle definition of trig functions a little bit.
