I can:-NAME ANGLES BASED ON THEIR NUMBER

OF DEGREES- DRAW AND BISECT ANGLES USING A

COMPASS

Warm Up 1/14/2013

Name 3 examples of angles in the real world.

History

The ancient Babylonians created several systems of measurement.

Historians believe that they were the first people to divide a circle into 360 equal parts, called degrees.

No matter who invented them, we all use degrees to measure angles.

Note that the numbers increase in a counter-clockwise direction…

90°

180° 0°360°

270°

Measuring Angles The symbol for a degree is °. An angle measurement of 10 degrees is

written 10°. To measure an angle you have to use a

protractor. A protractor is a tool shaped like half a

circle with markings from 0° to 180°.

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.

Now you are ready.

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

Once you reach 30° you need to be careful!!!

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

What does it measure?

This angle measures 35°.

You Try

Turn to page 15 in your textbook. Measure angle a. What did you get?

Classifying Angles

You can classify an angle using its measure.

An acute angle is an angle whose measure is greater than 0 and less than 90°.

Classifying Angles

Classifying Angles

A right angle is an angle whose measure = 90°.

Classifying Angles

Classifying Angles

An obtuse angle is an angle whose measure is greater than 90° and less than 180°.

Classifying Angles

Straight Angle

A straight angle is an angle whose measure = 180°.

Perpendicular Lines

Look again at the right angles. Lines that form right angles are said to

be perpendicular lines. The symbol for perpendicular lines is What 2 lines are perpendicular?

Practice

Complete pages 18-19 All You have 15 minutes. Homework: Workbook 5… You need a

protractor!!