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# Notes 1.4 Angle Measures - PowerPoint PPT Presentation

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

LT – I can find and compare angle measures.

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.

/ 1 by NUMBER

/ ABC by POINTS with vertex in the middle

/ CBA

/ B by VERTEX point

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

/ POR &

/ ROQ

or /O

NOT / ORQ ,

/ ORP,

Right = 90

Acute < 90

Straight = 180

Obtuse > 90

1.

2.

acute

right

3.

4.

?

acute

obtuse

?

5.

obtuse

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

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

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

Is this ready to measure the angle?

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.

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.