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Learn essential terms in circular trigonometry, coterminal angles, radian measure, and conversions between degrees and radians. Practice examples and deepen your understanding for improved test performance.
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Warm Up • How’d the test go? Better? Worse? • Did you do anything different to study for this test? • How many times have you attended tutoring? • Did you do every homework assignment for the unit?
Basic Terms • An angle is formed by rotating a ray around its endpoint. • The ray in its starting position is called the initial side of the angle. • The ray’s location after the rotation is the terminal side of the angle. terminal side angle initial side
Basic Terms • Positive angle: The rotation of the terminal side of an angle counterclockwise. • Negative angle: The rotation of the terminal side is clockwise.
A complete rotation of a ray results in an angle measuring 360. We don’t have to stop there! • 137 is coterminal with 497. They have the same terminal angle! We can keep adding or subtracting 360 to get more coterminal angles. 137 more 360 497 altogether!
Example 2: For the angles below, find the smallest positive coterminal angle. (Add or subtract 360 as may times as needed to obtain an angle with measure greater than 0 but less than 360.) a) 1115 b) 187 a) 1115° - 360° - 360° - 360° = 35° b) 187 + 360 = 173
What’s a radian? • You’re used to thinking of a circle in terms of degrees: 360° is the whole circle. 180° is half the circle, etc... • Radian measure is just a different way of talking about the circle. • Just as we can measure a football field in yards or feet--we can measure a circle in degrees or in radians!
Think about what the word radian sounds like… it sounds like “radius,” right? It turns out that a radian has a close relationship to the radius of a circle.
Example 3: Convert each degree measure to radians. (a) 30° (b) 120° (c) 60° (d) 270° (e) 104 °
Write these down in your notes! If you memorize them, it will make converting from radians to degrees (and vice versa) much easier!