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1.3 Measuring Angles

1.3 Measuring Angles. Stone High School: Geometry. Objectives:. Measure angles with a protractor. Identify and use the Angle Addition Postulate. Defining Angle Measure.

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1.3 Measuring Angles

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  1. 1.3 Measuring Angles Stone High School: Geometry

  2. Objectives: • Measure angles with a protractor. • Identify and use the Angle Addition Postulate.

  3. Defining Angle Measure A protractor is used to measure angles. As on a ruler, the intervals of a protractor must be equal. Then you can be sure that if the two angles have the same measure, then they are congruent.

  4. Look at example 1:

  5. Angles are measured in degrees. A protractor may thought of as another type of geometry ruler.

  6. Angle Congruence Postulate If two angles have the same measure, then they are congruent. If two angles are congruent, then they have the same measure.

  7. Example 3:

  8. P S R Angle Addition Postulate If point S is in the interior of angle PQR, then measure of angle PQS + measure of angle SQR = measure of angle PQR. Q

  9. Pairs of Angles • Complementary angles – are two angles whose measures have a sum on 90º. Each angle is called the complement of the other. • Supplementary angles – are two angles whose measures have a sum of 180º. Each angle is called the supplement of the other.

  10. Example 4: Name all complementary and supplementary angle pairs below. • Measure of angle A is 60 degrees: • Measure of angle B is 30 degrees: • Measure of angle C is 120 degrees.

  11. 1 2 Linear Pair Property • If two angles for a linear pair, then they are supplementary.

  12. Classification of Angles Definitions: Three Types of Angles A right angle is an angle whose measure is 90 degrees. An acute angle is an angle whose measure is less than 90 degree. An obtuse angle is an angle whose measure is greater than 90 degrees and less than 180 degrees.

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