Learning Goal: IWBAT to determine whether given side lengths form triangles

and solve for unknown angles in triangles.

Homework: HW 3.2: Triangle Inequality Worksheet HW 3.3A: Triangle Sum Theorem Worksheet

-------------------------------------------------------------------Do Now:

Find the measure of the unknown angles shown below.

September 6, 20131) Sit. 2) Materials out. 3) Backpacks away. 4) Do Now SILENTLY.

Agenda:

1. Do Now (10 min)

2.Explore Triangle Inequalities (15 min)

3.Triangle Inequality Theorem (30 min)

4.Constructing Triangles (15 min)

5.Triangle Proofs (15 min)

6.Whiteboard Activity (30 min)

7.Closure (5 min)

Triangle Experiment

Each pair will receive straws of different lengths

Select three straws with the given lengths and test whether the straws form a triangle.

Check off the “Yes” or “No” box.

Triangle Experiment

Try to find some common characteristics for the sets of side lengths that DO form a triangle.

Try to find some common characteristics for the sets of side lengths that DO NOT form a triangle.

Come up with a rule that can predict whether three side lengths will form a triangle.

Triangle Inequality Theorem

Triangle Inequality Theorem

Triangle Inequality Theorem

Triangle Inequality Theorem

Construct a Triangle

Construct a triangle that has side lengths 3 cm, 4 cm, and 5 cm.

Teacher will demonstrate to the class how to construct the triangle.

You can also follow the steps presented in the handout.

Construct a triangle with the following lengths. Some sets of given lengths will form triangles while others will not.

1 cm, 1cm, 2 cm

4 cm, 5cm, 2 cm

Review Triangle Theorems

Triangle Proofs

Given m<ABC = 30

m<BCA = 20

Prove m<DAE = 130B

C

A E

D

Triangle Algebra Activity

Students break up into groups of 3 or 4. Groups have been predetermined. Each group receives a whiteboard, marker, and eraser.

Teacher will present practice exercises about triangles on the board.

Your teams have 2 minutes to solve the problem and write the answer on the whiteboard with its justification.

The correct answer receives 1 point. The correct justification receives an additional point.

Geometry Period 2 Teams Red Team

1. George O.

2. Mayra R.

3. Charles L.

4. Ashley T.

Green Team

1. Ben M.

2. Kathy M.

3. Christian V.

4. Brisya C. Blue Team

1. Jose L.

2. Carina A.

3. Jackie D.

4. Miguel B.

Yellow Team

1. Oscar E.

2. Jazmin A.

3. Nancy L.

Purple Team

1. Linda

2. Jovanny H.

3. Adolfo G.

4. Justlene S. Orange Team

1. Ben L.

2. Susana A.

3. Abel P.

Geometry Period 4 Teams Red Team

1. Dennise P.

2. Amanda V.

3. Seth F.

4. Javier G.

Green Team

1. Veronica S.

2. Oscar S.

3. Lorena G.

4. Alfonso M.

Blue Team

1. Angie Z.

2. Miranda D.

3. Arthur D.

4. Sydney G.

Yellow Team

1. Jesus R.

2. Ariana P.

3. Leslie V.

4. Erick M.

Purple Team

1. James L.

2. Lee Ann Q.

3. Mirna A.

4. Thea Q. Orange Team

1. Christina G.

2. Derek A.

3. Yuleni V.

Geometry Period 6 Teams Red Team

1. Freddy A.

2. Anthony S.

3. Hannya O.

4. Ashley L.

Green Team

1. Christina R.

2. Geovanni B.

3. Oscar G.

4. Sabrina L. Blue Team

1. Jose S.

2. Jailene L.

3. Abigail G.

4. Andy H.

Yellow Team

1. Paulina C.

2. Martin R.

3. Melissa R.

4. Jonathan T.

Purple Team

1. Alexis A.

2. Deborah H.

3. Sabrina O.

4. Cristian B. Orange Team

1. Steven P.

2. Wendy G.

3. Abel P.

4. Leslie H.

Exercise #1

Find the measure of the unknown angle shown below.

Exercise #2

Find the measure of the unknown angle shown below.

Exercise #3

Find the measure of the unknown angle shown below.

Exercise #4

Find the measure of the unknown angle shown below.

Exercise #5

Find the measure of the unknown angle shown below.

Exercise #6

Find the measure of the unknown angle shown below.

Exercise #7

Find the measure of the unknown angle shown below.

Exercise #8

Find the measure of the unknown angle shown below.

Exercise #9

Find the measure of the unknown angle shown below.

Exercise #10

Find the measure of the unknown angle shown below.

Triangle Theorem Masters Period 1 Period 2

1. Miguel B.

2. Jose L.

3. Jackie D.

4. Carina

Period 4

1. Jesus R.

2. Ariana P.

3. Leslie V.

4. Eric M.

Period 5

Period 3

Period 6

1. Oscar G.

2. Christina R.

3. Sabrina L.

4. Geo B.

Closure

Take a moment to response to the following prompts on a flashcard.

Why do the angles of any triangle add up to 180 degrees?

The angles of any triangle add up to 180 degrees because ___________________________ .

What conditions must three sides satisfy in order for the sides to form a triangle?

In order for sides to form a triangle, _____________________ .