Point A location

Line

Line segment

Ray

A straight path that goes on forever in both directions.

A straight path between the points, called its endpoints.

A straight path that goes on forever in one direction from an endpoint.

Geometry Terms

End Point

If we look around us, we will see angles everywhere.

Angles In Daily Life

To name an angle, we name any point on one ray, then the vertex, and then any point on the other

ray.

For example: ABC or CBA

We may also name this angle only by the single letter of the vertex, for example B.

A

BC

Review Naming an Angle

There are four main types of angles.

Straight angle

Right angle

Acute angle Obtuse angle

A

B C

A

B C

A

B C

BA C

Review Types f Angles

Right angle: An angle whose measure is 90 degrees.

Right Angle Acute AngleStraight Angle Obtuse Angle

Examples Of Right Angle

Examples Of Obtuse Angle

Acute angle: An angle whose measure is less than 90 degrees.

Right Angle Acute AngleStraight Angle Obtuse Angle

Examples Of Acute Angle

Straight angle: An angle whose measure is 180 degrees.

Right Angle Acute AngleStraight Angle Obtuse Angle

Examples Of Straight Angle

Lines in a plane

What can you say about these pairs of lines?

These lines cross, or

intersect.

These lines do not intersect.

They are parallel.

Angles

Angles are measured in degrees.

A quarter turn measures 90°.

It is called a right angle.

We label a right angle with a small square called a square corner.

90°

Angles

A half turn measures 180°.

This is a straight angle180°

Angles

A full turn measures 360°.360°

Adjacent AnglesTwo angles that have a common vertex and a common ray are called adjacent angles. “SIDE BY SIDE”

C

D

B

A

Common ray

Common vertex

Adjacent Angles ABD and DBC

Adjacent angles do not overlap each other.

D

EF

A

B

C

ABC and DEF are not adjacent angles

More examples of adjacent angles.

55º

35º

50º130º

80º 45º

85º20º

Missing Angles

Our learning objectives today•To calculate missing angles on a straight line, around a point and in a triangle.

What do you need to know?Angles in a triangle add up to.................

180°

Angles on a straight line add up to.......180°

Angles around a point add up to.............360°

Complementary Angles

Two angles are called complementary angles if the sum of their degree measurements equals

90 degrees.

Example: These two angles are complementary.

                                                      

                        

These two angles can be “put" together to form a right angle which is

complementary!

                        

Supplementary AnglesTwo angles are called supplementary angles if the sum of their degree measurements equals

180 degrees.

Example: These two angles are supplementary.

                                                                      

These two angles can be “put" together to form a straight line!

                                                

Find the missing angle. You do not have a protractor.Use the clues in the pictures.

1.x

55

X=35

Find the missing angle. You do not have a protractor.Use the clues in the pictures.

2.165x

X=15

Calculate the missing straight line angle

69° 111°

Calculate the missing triangle angle

54°

89°

37°

Calculate the missing straight line angle

42°

103°35°