1.2: Poolroom Math

Geometry Warm-up

If B is the midpoint of line AC and the coordinates of A are (-8, 0) and the coordinates of B are (-2, 6), find the coordinates of point C. 1.

2. pg. 46 # 44

ANGLES

A Ray: part of a line, it has one endpoint and extends indefinitely in the other direction.

An Angle: the shape formed by two rays (sides of the angle) that start from one endpoint called the vertex.

A

B

C4

The angle is named by its vertex, by three points with the vertex in the middle, or by the number attached to the angle.

vertex

Practice Problems

How to Measure an Angle with a Protractor

STEP 1: Place the center of the protractor on the vertex of the angle.

STEP 2: Line up one of the sides of the angle with the 0 degree mark.

STEP 3: Find the measure of the angle by extending the other side. Remember: If the angle is obtuse, its measure will be > 90. If the angle is acute, its meaure will be < 90.

Practice with Protractor:

Turn to page 40 Example B. Remember to follow the steps!

TIP: sometimes it helps if you turn the paper upside down to measure with the protractor!

Why use the ≈ sign (approximately)?

pg. 43 # 15 to 19

Congruent Angles Remember the congruent sign (≅) when naming the angles!!!

Two angles are ≅ if they have tick marks OR the same measure (always degrees!)

38

38

Tick marks DO NOT go on the side!

Congruent Angles....

Some angles are bisected and form 2 ≅ angles

Name 3 angles, 3 rays, 2 ≅ anglesWhy can't you name the angles in this problem by ONLY the vertex letter?

Practice Naming Angles: pg. 41 Example C

What are 3 ways you KNOW that 2 angles are ≅ ?

Using your Algebra to find angle measures!

90

42 64

23

26x

y

z

Every straight line = 180 (arrow to arrow)

The "box" means 90 ALWAYS!

Now try pg. 42 # 1-37 odd