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Understanding, Naming, Measuring and Drawing Angles

M1, M7, G3, G7

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Angles – openings between intersecting lines or segments or rays

The amount of opening can vary.

Angles can be more open or less open than other angles.

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Units for angles.

The units for angles is degrees. It can be written with a word or a symbol.

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Straight Angles

An angle open to form a straight line is a straight angle.

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Right Angles . . . not wrong ones!

An angle that is like the corner of a square is called a right angle.

A right angle may open in any direction.

Right angle simply means “square corner.”

Sometimes we draw a small square in the angle to indicate that it is a right angle.

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Acute Angles

An angle whose opening is less than a right angle is an acute angle.

Isn’t it “a cute” little angle?

Opening smallerOpening larger

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Obtuse Angles

(That obtuse angle is sort of like a recliner.)

Bigger opening here!

Smaller opening here!

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Time to add a notebook page!

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Quick practice!

Which of these angles appears to be a right angle?

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Quick practice!

Which of these angles appears to be an acute angle?

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Quick practice!

Which of these angles appears to be an obtuse angle?

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Parts on an angle. A

G

W

vertex

Interior – the part of the angle that is between the rays or segments of an angle

Exterior – anything on the outside of the angle

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Naming an angle.

A

G

W

Use three letters to name an angle. Always put the vertex in the middle.

The name for this angle is GAW . . . or WAG or A

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Another notebook page!

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What part of the angle?

A

G

W

a. interiorb. vertexc. raysd. exterior

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Which part of an angle?

A

G

W

a. interiorb. vertexc. raysd. exterior

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Which part of the angle?

A

G

W

a. interiorb. vertexc. raysd. exterior

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The name for this angle is . . .

v

t

q

a. q b. qvt c. qtv

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Measuring Angles

A protractor is used to measure angles. 

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The two scales make it easy for us to measure angles facing different ways.

Can you find the two scales on your protractor?

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Two scales.

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Look at the first angle in your packet for the next couple of slides.

You need a protractor and a pencil.

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To measure the size of an angle, place the protractor over angle a so that the center of the protractor is directly over the vertex.

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Make sure the segment next to the vertex is lined up on one ray of the angle.

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The other ray of your angle passes through the scale of the protractor somewhere on the outside.

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A protractor has two sets of numbers.

In the angle is acute, read the number less than 90 degrees.If the angle is obtuse, read the number greater than 90 degrees.

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Now you measure your first angle.

1. Put the circle on the vertex. 2. Line up the segment by the circle with the ray

of your angle. 3. Hold your protractor steady and read the

number where the other ray passes on the scale. 4. Use the smaller number if the angle is acute,

the larger number if it’s obtuse. 5. Write the measure of the angle in the interior

of the angle.

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Drawing angles.

Follow the instructions in your packet. 1. Draw a long segment. Make a dot at one end. 2. Center the protractor over the dot. Line it up

so that the segment passes through the 0 degree mark.

3. Find the number that matches the size of the angle you wish to draw (use the correct scale), and draw a dot at that number.

4. Connect the dots with your straight edge. 5. Put the degrees in the interior of the angle.

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And have fun with measuring and drawing angles!