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Measuring Angles

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Math Message

Max measured an angle. He said the angle was 4 centimeters wide. Does his measurement make sense?

Why or why not?

Attributes (features) of angle size

• An angle's size depends on the spread of the angle's rays.

• The spread can be thought of in terms or turns, or rotations

• The degree is the standard unit for measuring angle size

Acute Angles

Acute angles are SMALLER than a right angle.

They measure between

0° - 89°

 

Acute Triangles

A triangle with THREE acute angles.

 

Right Angles

Acute angles are SMALLER than a right angle.

They measure 90°

 

Right Triangles

A triangle that has ONE right angle.

 

Obtuse Angles

Obtuse angles are BIGGER than a right angle.

They measure between 91°-179°

 

Obtuse Triangles

Any triangle that has ONE obtuse angle.

 

Multiple Choice

What Type of Triangle is this?

• Acute Triangle

• Right triangle

• Obtuse Triangle

Multiple Choice

What Type of Triangle is this?

• Right triangle

• Equilateral triangle

• Obtuse Triangle

• Acute Triangle

Multiple Choice

What Type of Triangle is this?

• Right Angled triangle

• Obtuse triangle

• Acute Triangle

Multiple Choice

Which angle type is pictured?

• Acute
• Right
• Obtuse
• Straight

Multiple Choice

Which type of angle is pictured?

• Acute
• Right
• Obtuse
• Straight

Multiple Choice

What is the measure of ∠DEF

in the figure below?

• 40 degrees

• 80 degrees

• 90 degrees

• 140 degrees

Multiple Choice

Which angle measures about 20 degrees?

Multiple Choice

Which of the following books is open 180°?

Measuring Angles

What would we need in a tool that could measure angles?

Measuring Angles

1. The tool would be made up of angles

2. All of the unit angles would be the same size

3. The units would be numbered

https://www.youtube.com/watch?v=_erF7VM5-zI

Math Journal page 213

• What type of angle is Angle A?

• Align the middle mark on the measurer over the angle's vertex. 

• Look in the direction of the arc. Read the degree measure where the other side of the angle crosses the edge of the measurer.