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• Let’s Review! Line Ray Line Segment Angle Vertex Point Triangles Intersection

1.2 Measurement of Segments and Angles

Measuring segments:

Ruler or meter stick units of measure

Match item being measured with proper unitU.S.: Inches, feet, yards, miles etc.Metric: km, cm, m, mm

Distance: absolute value

m AB1 2 3 4

A B

|2-3| or |3-2|

= |-1| = |1|

= 1 = 1

The length of AB = 1 cm

cm

Measuring angles:

Unit of measure:

Degrees

Tool: protractor

Angle measurement

Angle measurement is the opening from one ray to the next ray.

We usually use the inside measurement, 180 degrees or less.A full turn is a circle and measures 360 degrees.

P

A R

m<PAR = 90m<A = 90

Angle measurement

m<1 = 1351

Let’s think about the measure of the angle formed by the hands of a clock at 3:00 and 4:30

Classify angles by size

Acute: 0<90

Right: 90

Obtuse: 90<180

Straight: 180

Parts of a degree:

1 Degree = 60’ (minutes)1 Minute = 60” (seconds)So, 87 = 8730’

1

2

90 = 8959’60”

Find m<CBD

A

B

C

D

m<ABD = 90

m<ABC = 7421’10”

90

- 7421’ 10”

1538’50”

Congruent angles and segments

Symbol: =

= < have the same measure

= have the same length

<A = <B

A 60 B 60

Congruency

Tick marks show congruencyA

C

B

X

Z Y

Can you name congruent angles and segments?

Example

AB

C

1

2

m<ABC = 90

m<1 = (3x+4)

m<2 = (x+6)Find both angles!3x + 4 + x + 6 = 90 so m < 1 = 64

4x + 10 = 90 m < 2 = 26

4x = 80

X = 20

Recap!

Acute AngleCongruent AngleCongruent SegmentsDegreeObtuse AngleRight Angle

YOUR TURN

Work with a partner

Pg 14 #1,2, 5-8, 10, 12, 13-16, 18