Trigonometry: The unit circle, Sine, and Cosine
 This is a free lesson from our course in Trigonometry

 In this lesson you'll learn the relationship of Sine and Cosine to the Unit Circle. It is explained with the help of examples, video and explanation by instructor in own hand writing and covers practice questions with solution. A circle with center at the origin and radius 1 is called the unit circle and has the equation x2 + y2 = 1. Using the unit circle, you'll gain understanding of some of the properties, such as domain, range and asymptotes (if any), of the trigonometric functions. Let be the measure of central angle and P (x, y) the point on the unit circle. If the ray from the origin (0, 0) to (x, y) makes an angle from the positive x-axis, then    sin  = y    cos  = x Therefore, the coordinates of P are (cos , sin ).
Other useful lessons:
 Definitions of Trigonometric Functions Graphs of Sine and Cosine Functions
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