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Standard. G.G.13. Apply properties of angles, parallel lines, arcs, radii, chords, tangents, and secants to solve problems. 1.4: Measure and Classify Angles 1.5: Describe Angle Pair Relationships. Objectives: By the end of this lesson I will be able to :
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Standard G.G.13. Apply properties of angles, parallel lines, arcs, radii, chords, tangents, and secants to solve problems.
1.4: Measure and Classify Angles1.5: Describe Angle Pair Relationships Objectives: By the end of this lesson I will be able to : • To define, classify, draw, name, and measure various angles • To use the Protractor and Angle Addition Postulates • To use special angle relationships to find angle measures
Angle • An angle consists of two different rays (sides) that share a common endpoint (vertex). • Angle ABC, ABC, or B Vertex Sides A “Rabbit Ear” antenna is a physical model of an angle
Angle • An angle consists of two different rays (sides) that share a common endpoint (vertex). • Angle ABC, ABC, or B
Example 1 How many angles can be seen in the diagram? Name all the angles. 3 <WXY <YXZ <WXZ
How Big is an Angle? Is the angle between the two hands of the wristwatch smaller than the angle between the hands of the large clock? • Both clocks read 9:36 Click me to learn more about measuring angles
Measure of an Angle The measure of an angle is the smallest amount of rotation about the vertex from one side to the other, measured in degrees. • Can be any value between 0 and 180 • Measured with a protractor
The measure of this angle is written: How To Use a Protractor
Example 2 Use the diagram to fine the measure of the indicated angle. Then classify the angle. • KHJ • GHK • GHJ • GHL = 55 = 125 = 180 = 90
Example 3 . Use your protractor to measure the angles shown for exercises 3-5.
Example 4 What is the measure of DOZ?
Example 4 You basically used the Angle Addition Postulate to get the measure of the angle, where mDOG + mGOZ = mDOZ.
Angle Addition Postulate If P is in the interior of RST, then mRST= mRSP + mPST.
Example 5 Given that mLKN = 145°, find mLKM and mMKN.
Congruent Angles • Two angles are congruent angles if they have the same measure. Add the appropriate markings to your picture.
Angle Bisector An angle bisector is a ray that divides an angle into two congruent angles.
Example 6 In the diagram, YW bisects XYZ, and mXYW = 18°. Find mXYZ.
Angle Pair Investigation In this Investigation, you will be shown examples and non-examples of various angle pairs. Use the pictures to come up with a definition of each angle pair.
Linear Pairs of Angles • Two adjacent angles form a linear pair if their noncommon sides are opposite rays. • The angles in a linear pair are supplementary.
Vertical Angles • Two nonadjacent angles are vertical angles if their sides form two pairs of opposite rays. • Vertical angles are formed by two intersecting lines.
Example 7 • Given that 1 is a complement of 2 and m1 = 68°, find m2. • Given that 3 is a complement of 4 and m3 = 56°, find m4.
Example 8 Identify all of the linear pairs of angles and all of the vertical angles in the figure.
Example 9 Two angles form a linear pair. The measure of one angle is 5 times the measure of the other angle. Find the measure of each angle.