Lines and Angles

Lines are everywhere…

Line segments can be measured from beginning to end.

We mark a line segment with points

Those points are labeled with letters

A B

We can name this line segment either:

AB BA

Lines are different from line segments.We can see the beginning and ending of a line segment.Lines extend on forever

To show the difference between a line and a line segment we use arrows instead of points

Lines vs. Line Segments

A B

We name a line by showing the arrows: AB

A

B

C

D

Two line segments are shown here

AB CD

When lines or line segments meet…

A

B

C

D

They intersect to form angles…

C

DA

B

The point at the intersection is called the vertex.

E

When we name the angle, the vertex must be in the middle

C

DA

B

The point at the intersection is called the vertex.

E

When we name the angle, the vertex must be in the middle

AED or

DEA

Point E, the vertex, is always in the middle

Notice any angles?

H

J

I

A

B

C

XY

Z

P

Q

R

Name these angles…

BAC

XYZ

PQR

JHI

A

B

C

D

When 2 line segments meet to form a 90° angle they called perpendicular line segments

A

B

C D

Perpendicular lines intersect to form a 90° angle also referred to as a right angle.You can check if the angle right by holding up a piece of notebook paper.

90°90°

90°90°

90°

Where do we see right angles?

PerpendicularA

B

C D

A

B

C D

Perpendicular

Where do we see right angles?

Let’s Look at the Strata Center again…

Notice many perpendicular lines?

A

B

C D A

B

C

D

Not quite 90°

Smaller than 90° again.

A

B

C D A

B

C

D

A

B

C D A B

CD

A

B

C D A B

CD

Both of these angles are smaller than 90° Angles smaller than 90° are called acute

Acute Angle = Less than 90°

What about angles larger than 90°?

What about angles larger than 90°?

Notice all of the extra room?

Angles larger than 90° are called obtuse

If you extend these two lines segments will they ever touch?

Right, if they did what might happen?

When two line segments on the same plane never touch they are called

Parallel

Lots of parallel lines

Do these lines intersect?

But, if you extend them outward, would they intersect?

Are these lines parallel?

No, but actually they are. It’s just the angle of the picture.

Examples of Parallel Lines