Sec. 1.4 Measure and Classify Angles

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Sec. 1.4 Measure and Classify Angles

• An angle consists of two different rays with the
  same endpoint.
• The rays are the sides of the angle.
• The endpoint is the vertex of the angle.

This angle can be named ?BAC, ?CAB, or ?A. Point
A is the vertex of the angle.
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EXAMPLE 1
Name angles
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• A protractor can be used to approximate the
  measure of an angle.
• An angle is measured in units called degrees
• (ex 90).

We write the measure of an angle as m?ABC 90
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Classifying Angles

• Angles can be classified as acute, right, obtuse,
  and straight.

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EXAMPLE 2
Measure and classify angles
Use the diagram to find the measure of the
indicated angle. Then classify the angle.
SOLUTION
A protractor has an inner and an outer scale.
When you measure an angle, check to see which
scale to use.
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EXAMPLE 2
Measure and classify angles
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for Examples 1and 2
GUIDED PRACTICE
1. Name all the angles in the diagram above.
Which angle is a right angle?
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Postulate 4 Angle Addition Postulate
If P is in the interior of ?RST, then m?RST
m?RSP m?PST Very similar to which postulate?

• Two angles are congruent angles if they have the
  same measure.

Angles are congruent ?A ? ?B
Angle measures are equal m?A m?B
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Find angle measures
EXAMPLE 3
Angle Addition Postulate
Substitute angle measures.
145 6x 7
Combine like terms.
Subtract 7 from each side.
138 6x
Divide each side by 6.
23 x
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EXAMPLE 3
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Given that ?EFG is a right angle, find m ?EFH
and m ? HFG.
GUIDED PRACTICE
Combine like terms.
Subtract 3 from each side.
Divide each side by 3.
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• An angle bisector is a ray that divides an angle
  into two angles that are congruent.

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EXAMPLE 5
Double an angle measure
SOLUTION
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Homeworkp. 28-314-26 even, 30-38 all, 40,53,54