The Unit Circle – Part I establishes the connection between angles measured counterclockwise from the positive side of the x-axis and points on a circle of radius 1 and formalizes this as a function from angles to points (ordered pairs). From this, the sin and cos functions are defined. Value of sin and cos are found for angles which are multiples of 90°. Values which come from the 30° – 60° – 90° triangle and the 45° – 45° – 90° triangle are presented in the Unit Circle – Part II lesson.
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