Lesson 1 4 Angles Lesson 1 4 Angles
- Slides: 13
Lesson 1 -4 Angles Lesson 1 -4: Angles 1
Angle and Points l An Angle is a figure formed by two rays with a common endpoint, called the vertex. ray vertex l ray Angles can have points in the interior, in the exterior or on the angle. A E B D C Points A, B and C are on the angle. D is in the interior and E is in the exterior. B is the vertex. Lesson 1 -4: Angles 2
Naming an angle: (1) Using 3 points (2) Using 1 point (3) Using a number – next slide 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. B Lesson 1 -4: Angles A C 3
Naming an Angle - continued Using a number: A number (without a degree symbol) may be used as the label or name of the angle. This A number is placed in the interior of the angle near its vertex. The angle to the left can be named B 2 C as. * The “ 1 letter” name is unacceptable when … more than one angle has the same vertex point. In this case, use three letter name or a number if it is present. Lesson 1 -4: Angles 4
Example l K is the vertex of more than one angle. Therefore, there is NO in this diagram. There is Lesson 1 -4: Angles 5
4 Types of 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 . Lesson 1 -4: Angles 6
Measuring Angles l Just as we can measure segments, we can also measure angles. l We use units called degrees to measure angles. • A circle measures _____ 360º ? • 180 A (semi) half-circle measures _____ ? º • ? A quarter-circle measures _____ 90º • One degree is the angle measure of 1/360 th of a circle. Lesson 1 -4: Angles 7
Adding Angles l l When you want to add angles, use the notation m 1, meaning the measure of 1. If you add m 1 + m 2, what is your result? m 1 + m 2 = 58. m 1 + m 2 = m ADC also. Therefore, m ADC = 58. Lesson 1 -4: Angles 8
Angle Addition Postulate: The sum of the two smaller angles will always equal the measure of the larger angle. Complete: m MRK ____ + m KRW ____ = m MRW _____ Lesson 1 -4: Angles 9
Example: Angle Addition K is interior to MRW, m MRK = (3 x) , m KRW = (x + 6) and m MRW = 90º. Find m MRK. First, draw it! 3 x 3 x + 6 = 90 4 x + 6 = 90 – 6 = – 6 4 x = 84 x = 21 x+6 Are we done? m MRK = 3 x = 3 • 21 = 63º Lesson 1 -4: Angles 10
Angle Bisector An angle bisector is a ray in the interior of an angle that splits the angle into two congruent angles. Example: Since 4 6, is an angle bisector. 5 3 Lesson 1 -4: Angles 11
Congruent Angles 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: 3 5. Lesson 1 -4: Angles 12
Example l Draw your own diagram and answer this question: If is the angle bisector of PMY and m PML = 87 , then find: m PMY = _______ l m LMY = _______ l l Lesson 1 -4: Angles 13
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