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 Team1. George O.2. Mayra R.3. Charles L. 4. Ashley T.

Green Team1. Ben M.2. Kathy M.3. Christian V. 4. Brisya C.

Blue Team1. Jose L.2. Carina A.3. Jackie D.4. Miguel B.

Yellow Team1. Oscar E.2. Jazmin A.3. Nancy L.

Purple Team1. Linda2. Jovanny H.3. Adolfo G. 4. Justlene S. Orange Team1. Ben L.2. Susana A.3. Abel P.

Geometry Period 4 Teams Red Team1. Dennise P.2. Amanda V.3. Seth F.4. Javier G.

Green Team1. Veronica S.2. Oscar S.3. Lorena G.4. Alfonso M.

Blue Team1. Angie Z.2. Miranda D.3. Arthur D.4. Sydney G.

Yellow Team1. Jesus R.2. Ariana P.3. Leslie V. 4. Erick M.

Purple Team1. James L.2. Lee Ann Q.3. Mirna A.4. Thea Q. Orange Team1. Christina G.2. Derek A.3. Yuleni V.

Geometry Period 6 Teams Red Team1. Freddy A.2. Anthony S.3. Hannya O. 4. Ashley L.

Green Team1. Christina R.2. Geovanni B. 3. Oscar G.4. Sabrina L.

Blue Team1. Jose S.2. Jailene L.3. Abigail G.4. Andy H.

Yellow Team1. Paulina C.2. Martin R.3. Melissa R.4. Jonathan T.

Purple Team1. Alexis A.2. Deborah H.3. Sabrina O. 4. Cristian B. Orange Team1. 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 41. Jesus R.2. Ariana P.3. Leslie V. 4. Eric M.

Period 5

Period 3

Period 61. Oscar G.2. Christina R.3. Sabrina L.4. Geo B.

ClosureTake 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, _____________________

.