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Notes 1.4 Angle Measures. LT – I can find and compare angle measures. Definition of an Angle. Angle – formed by two rays with the same endpoint . The rays are the sides or legs of the angle and the endpoint is the vertex. vertex. A. Naming an Angle.

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notes 1 4 angle measures
Notes 1.4 Angle Measures

LT – I can find and compare angle measures.

slide2

Definition of an Angle

Angle – formed by two rays with the same endpoint. The rays are the sides or legs of the angle and the endpoint is the vertex.

vertex

A. Naming an Angle

The name can be the numberbetween the sides of the angle: /3.

The name can be the vertexof the angle: /G.

The name can be three points that include on each ray with the vertex

written in the middle/AGCor / CGA.

example 1 name the angle 4 ways
Example 1: Name the angle 4 ways.

/ 1 by NUMBER

/ ABC by POINTS with vertex in the middle

/ CBA

/ B by VERTEX point

example 2 name the adjacent angles
Example 2: Name the Adjacent Angles

These angles are called “adjacent” which means “next to” because they share a ray.

/ POR &

/ ROQ

or /O

NOT / ORQ ,

/ ORP,

slide5

B. Classifying Angles

Right = 90

Acute < 90

Straight = 180

Obtuse > 90

slide6

State whether the following are acute, right, or obtuse.

1.

2.

acute

right

3.

4.

?

acute

obtuse

?

5.

obtuse

slide7

C. Angle Addition Postulate

Example 1 Suppose that m/1 = 42 and m/ ABC= 88. Find m/2.

88°

m/1 + m/2 = m/ ABC

42°

42 + m/2 = 88

m/2 = 46

slide9

D. Congruent Angles

Angles with the same measure are congruent. Congruent angles are marked by arcs.

Example 1 Find m/GXF and m/IXJ

5x + 3 = 7x – 9

-5x -5x

3 = 2x – 9

+9 +9

12 = 2x

2 2

6 = x

m/GXF = 5(6) + 3 = 33°

m/IXJ = 7(6) – 9 = 33°

7x - 9

5x + 3

when we use a protractor we need to line it up correctly
When we use a protractor, we need to line it up correctly.

You need to make sure the protractor is lined up correctly.

Is this ready to measure the angle?

were you right it wasn t
Were you right......................it wasn’t

Look for the upside down ‘T’ in the middle of the straight line on your protractor.

This needs to be exactly on the vertex of your angle.

slide12

We need to remember.....

It doesn’t

matter which

way round the

angle is, you

ALWAYS need

to line the upside

down ‘T’ to the vertex

of the angle.

now you are ready
Now you are ready.

Read from the 0°, and follow the inner set of numbers.

once you reach 30 you need to be careful
Once you reach 30° you need to be careful!!!

You then need to look at the 1° markings on the outer set of numbers.

what does it measure
What does it measure?

This angle measures 35°.

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