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Unit Circle
CONCEPTS
Properties of a Unit Circle
• When given a value for cos, sin, or tan, recall there are certain angle ranges where the result is positive or negative
• The radius of the unit circle = 1
• The sign of cos, sin, and tan can be found by drawing the angle on the circle and then use the signs as referenced by the axis at 90°, 180°, 270°, and 360°
PRACTICE PROBLEMS
Question 1 If 180° < θ < 270° and sin θ = -12/13, then cos θ = ?
-- Answer -- -5/13
sin θ and cos θ are both negative between 180° to 270°
Question 2 When sin θ = -1, the value of cos θ = ?
-- Answer -- 0°
sin 0° = 0 => cos 0° = 1
sin 90° = 1 => cos 90° = 0
sin 180° = 0 => cos 180° = -1
sin 270° = -1 => cos 270° = 0
ACT PRACTICE PROBLEMS
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