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1-4: Measuring Angles

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1-4: Measuring Angles

- An angle is formed by two rays with the same endpoint.
- The rays are the sides of the angle and the endpoint is the vertex of the angle.
- The interior of an angle is the region containing all points between the sides of the angle.
- The exterior of an angle is the region containing all points outside the angle.

- 3 Ways to name an angle
1. by its vertex (A)

2. by a point on each ray

and the vertex

(BAC or CAB),

3. by a number (1).

*Note: When using 3 points to name an angle, the vertex must go in the middle!

- What are two other names for 1?
- What are two other names for KML?

- One way to measure the size of an angle is in degrees.
- To say that the measure of A is 62, you would write mA = 62.
Protractor Postulate: Consider OB and point A on one side of OB. Every ray of the form OA can be paired one to one with a real number from 0 to 180.

- You can classify angles according to their measures.

Symbol for right angle!

- What are the measures of LKN, JKL, and JKN?
- Classify each as acute, right, obtuse, or straight.

- Angles with the same measure are congruent angles.
- This means that if mA= mB, then A B (and vice versa).
- You can mark angles with arcs to show they are congruent.

Angle Addition Postulate: If point B is in the interior of AOC, then mAOB + mBOC = mAOC.

- If mRQT = 155, what are mRQS and mTQS?