Exploring the Triangle Angle Sum Theorem

The video tutorial provides a visual proof of the triangle angle sum theorem, demonstrating that the sum of the angles in a triangle is 180 degrees. The lesson begins with an introduction to the theorem and the materials needed for the proof. It then guides students through constructing and completing the visual proof using paper, a straight edge, and scissors. The tutorial concludes with practice problems to reinforce the concept, helping students apply the theorem to find missing angles in various triangles.

What is the sum of the interior angles of a triangle?

• 360 degrees

• 270 degrees

• 180 degrees

• 90 degrees

Tags

CCSS.8.G.A.5

What type of geometry do we study in high school?

• Hyperbolic geometry

• Spherical geometry

• Non-Euclidean geometry

• Euclidean geometry

Which of the following items is NOT needed for the visual proof?

• Three sheets of paper

• A pen or pencil

• A protractor

• A pair of scissors

Where should you place the line on your paper when starting the proof?

• On the left side of the paper

• In the middle or lower half of the paper

• At the top of the paper

• On the right side of the paper

What should be the approximate size of the triangle you draw?

• The size of your head

• The size of your foot

• The size of your hand

• The size of your thumb

Tags

CCSS.4.G.A.1

What should you do after drawing and measuring the triangle?

• Color the triangle

• Cut out the triangle

• Fold the triangle

• Erase the triangle

Tags

CCSS.4.G.A.1

What happens to the measure of an angle when you tear it off the triangle?

• It increases

• It becomes zero

• It decreases

• It remains the same

Tags

CCSS.4.MD.C.5B

CCSS.HSG.CO.A.1

What do you do with the three angles after tearing them off the triangle?

• Throw them away

• Line them up on a straight line

• Glue them back together

• Measure them again

In the first practice problem, if one angle is 30 degrees and another is 110 degrees, what is the measure of the third angle?

• 40 degrees

• 30 degrees

• 60 degrees

• 50 degrees

Tags

CCSS.8.G.A.5

In an isosceles triangle, if one angle is 68 degrees, what is the measure of each of the base angles?

• 68 degrees

• 90 degrees

• 56 degrees

• 72 degrees

Tags

CCSS.8.G.A.5