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# 1-4: Measuring Angles - PowerPoint PPT Presentation

1-4: Measuring Angles. Parts of an Angle. 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.

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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 mA = 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 mA= mB, 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 mAOB + mBOC = mAOC.

• If mRQT = 155, what are mRQS and mTQS?

 If mABC = 175, what are mABD and mCBD?