09 - Unit Circle - Definition & Meaning - Sin(x), Cos(x), Tan(x), - Sine, Cosine & Tangent

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In this lesson, we will learn what a unit circle is and why it is crucial to master in trigonometry, pre-calculus, and calculus. The unit circle is a circle of radius 1 (a unit radius) that is superimposed on to an xy plane. The points on the circle itself represent the sine and cosine values of the angles around the unit circle. In this lesson, we will spend our time finding the sine and cosine of the angles in quadrant one, and we will fill out a table of trigonometric functions at each of these angles. This is critical to master as understanding the first quadrant will help us find trig functions at any other angle around the unit circle.