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Measuring Angles. Lesson 1.3. Big angle vs. Little angle. Definition of degree. Degrees were developed by the Babylonians thousands of years ago. They divided a circle into 360 parts and called each part one degree. Notation for angle measurement.
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Measuring Angles Lesson 1.3
Definition of degree Degrees were developed by the Babylonians thousands of years ago. They divided a circle into 360 parts and called each part one degree.
Notation for angle measurement The symbol for degrees, as you probably already know, is a small superscript circle. 45° 112° 37°
Classification of Angles • Acute Angles • Right Angles • Obtuse Angles • Straight Angles
Definition • Acute angles angles that measure less than 90°
Definition • Right angles angles that measure 90° Symbol for right angles
Definition • Obtuse angles angles that measure more than 90° but less than 180°
Definition • Straight angle an angle that makes a straight line and measure 180°
Angle congruence Angles are congruent if they have the same measure 48° A 48° B
Angle congruence Angles are congruent if one can be moved onto the other so that they match exactly.
Marking Congruent Angles and Sides with Tick Marks. A D B C E F AB DE A D BC EF B E C F AC DF
Pairs of Angles • Complementary Angles • Supplementary Angles • Linear Pair
Definition • Complementary angles Two angles that total 90 degrees 30 and 60 27 and 63 12 and 78
Definition • Supplementary angles Two angles that total 180 degrees • and 155 • 67 and 113 • 124 and 56
Definition • Linear angles Two angles that share a side and make a line. Linear angles total 180° Similar to Supplementary
Angle addition postulate If point S is in the interior (middle) of angle PQR, then the measure of PQS + measure of SQR = measure of PQR S P Q R
Angle addition postulate • Practice Problems • Page 32 # 36-44
Assignment • A4 • Worksheet 1.3 • pp. 30-32 # 13, 27-44