13.2 angles and angle measure objectives: 1.change radian measure to degree measure and vice-versa....
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13.2 Angles and Angle Measure
Objectives:1. Change radian measure to degree
measure and vice-versa.2. Identify coterminal angles.
Angles on a coordinate plane
Parts of an angle on a coordinate plane:Initial side – a ray fixed along the positive x-axisTerminal side – the other ray that can rotate about the centerStandard Position – when the vertex is at the origin and the initial side is on the positive x-axis
Types of measures
Positive Angle
225°
Negative Angle
-135°
Angles more than 360°For each revolution, add 360°, plus the other
angle.The angle is 130°+360°=
490°.
Drawing AnglesDraw an angle with the
given measure in standard position.
1. 210°2. 540°
540-360=1803. -45°
1.
2.
3.
Radians
• Radian measure is another unit used to measure angles.
• It is based on the concept of a unit circle which is a circle with a radius of 1 whose center is at the origin.
• If the radius is 1, the circumference is 2π so 2π is the same as 360°. Smaller angles are fractional parts of 2π.
Unit Circle
Changing from radians to degrees or from degrees to radians
Radians to degrees – Multiply the number of
radians by
Example:
Degrees to radians – Multiply the number of
degrees by
Example: 75°
180
5
4
5 180
4
225
180
75180
5
12
Coterminal Angles
Coterminal Angles are angles in standard position with the same terminal side such as 30° and 390°.
To find additional angles with the same coterminal angle, add multiples of 360 or subtract multiples of 360. For radian measure, add multiples of 2π or subtract multiples of 2π.
Example:
Find one angle with positive measure and one angle with negative measure coterminal with each angle.
1. 210°210+360=570°210-360=-150°
2. 73
7 7 6 132
3 3 3 3
7 6
3 3 36 5
3 3 3
Homeworkp. 712
20-54 even
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