3. Naming an angle: (1) Using 3 points (2) Using 1 point (3) Using a number – next slide Lesson 1-4: Angles Using 3 points: vertex must be the middle letter This angle can be named as Using 1 point: using only vertex letter * Use this method is permitted when the vertex point is the vertex of one and only one angle. Since B is the vertex of only this angle, this can also be called . A B C
4. Naming an Angle - continued Lesson 1-4: Angles Using a number: A number (without a degree symbol) may be used as the label or name of the angle. This number is placed in the interior of the angle near its vertex. The angle to the left can be named as . * The “1 letter” name is unacceptable when … more than one angle has the same vertex point. In this case, use the three letter name or a number if it is present. 2 A B C
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6. 4 Types of Angles Lesson 1-4: Angles Acute Angle: an angle whose measure is less than 90 . Right Angle: an angle whose measure is exactly 90 . Obtuse Angle: an angle whose measure is between 90 and 180 . Straight Angle: an angle that is exactly 180 .
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9. Angle Addition Postulate Lesson 1-4: Angles The sum of the two smaller angles will always equal the measure of the larger angle . Complete: m ____ + m ____ = m _____ MRK KRW MRW Postulate:
10. Example: Angle Addition Lesson 1-4: Angles 3x + x + 6 = 90 4x + 6 = 90 – 6 = –6 4x = 84 x = 21 K is interior to MRW, m MRK = (3x) , m KRW = (x + 6) and m MRW = 90 º. Find m MRK. 3x x+6 Are we done? m MRK = 3x = 3 • 21 = 63 º First, draw it!
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12. Congruent Angles Lesson 1-4: Angles 3 5. 5 3 Definition: If two angles have the same measure, then they are congruent. Congruent angles are marked with the same number of “arcs”. The symbol for congruence is Example:
![Angle and Points ,[object Object],Lesson 1-4: Angles vertex ray ray ,[object Object],Points A, B and C are on the angle. D is in the interior and E is in the exterior. B is the vertex. A B C D E](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)