Angles and Line Segments

By

Teacher Angelo

Angle – is the union of two none-collinear rays or segments having the common end point called vertex.

Line SegmentVertex O

AngleLine Segmen

t

Types of an angle

Right Angle

90 ̊

-With measure of exactly 90 ̊

Acute Angle -With measure of less than 90 ̊

40 ̊

Obtuse Angle - With measure of more than 90 ̊ but less than 180 ̊

155 ̊

Straight Angle -With measure of exactly 180 ̊

180 ̊

Reflex Angle - With measure of more than 180 ̊ but less than 360 ̊

200 ̊

Measuring, calculating and drawing angles...

What do we use to measure an angle?

A protractor

A standard protractor to use in the classroom.

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

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.

We need to remember.....

It doesn’t matter which way round the angle is, you ALWAYS need to line the upsidedown ‘T’ to the vertexof the angle.

Reading the angle measure.

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

Be careful in reading between tens.

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

What does it measure?

This angle measures 35°.

How to measure an Angle?

How to Draw an Angle?

Dividing Angles and Line segments in half

A. Using a protractor

Steps

1. Measure the size of the given angle.

2. Divide into half

3. Draw a straight line to divide the angle into half.

B. Using a compass to divide the angle into half

Steps

1.Place the needle of the compass at the vertex of the angle.

2. Open the compass about one third of the length of the side of the angle.

3. Draw an arc that intersects at two points on the sides of the angle. Name them as any letter.

4. Use the points of intersection on the sides of the angle as the center and draw same arc.5. Mark the intersection of the arcs with any letter.6. Draw straight line joining the intersection of the arcs and the vertex of the angle that divides the angle into two equal parts.

How To Bisect an Angle?

Using a ruler to divide a line segment into half.Steps1. Measure the length of the line segment. 2. Divide the line segment into half. 3. Mark and name the mid-point by any letter that shows the half of the line segment.

Answer the Exercise on the Workbook letter F, page 107

Using a compass to divide a line segment.Steps1. Open the compass slightly more than the length of the line segment.2. Draw arcs with the end points of the line segments as the center. Name the intersections of the arcs with any different letters,

3. Draw a dotted or broken line segments joining the intersections of the two arcs. 4. Name the intersection of the line segment and the broken line with any letter showing the half of the line segment.

How to Bisect a line SegmentUsing a Compass?

Vocabulary and Spelling Test+

Lesson 3 Test