Geometry Lesson Help: Proving Triangles Are Congruent

Congruent Triangles Lesson #3: Proving Triangles Congruent(SSS, SAS)

Context

This is the third lesson of the unit. Students will need to recall angle relationship theorems and the reflexive property in order to identify congruent triangles using the postulates in this section. Students will need to understand how to write a congruence statement.

Objectives Students will be able to prove triangles are congruent using the Side-Side-Side and Side-Angle-Side congruence postulates.

Resources, Media and Technology

6 toothpicks a piece for every student

Procedures
To start class, I will check homework and then ask if anyone has any questions over the homework. If not, I will pass out the quizzes. I will be walking around the room making sure that everyone is doing their own work and answering any questions that anyone might have. After all the quizzes have been turned in, I will proceed with the next lesson. First, I will pass out six toothpicks to every student in class. I instruct the students to form a triangle with the toothpicks, such that the tips of the toothpicks are touching each other. Then I will ask the students if they can form another triangle using the same length toothpicks. Some will try and say that they can, but it is probably because they are incorrectly manipulating the toothpicks.

Next, have them form another triangle using the other three same length toothpicks. I will ask them if those triangles are congruent. Since they are and the students could not form another triangle using the same length toothpicks, I will tell them that they just proved the Side-Side-Side Triangle Congruence Theorem. I will write SSS on the board and define the postulate. I will do the same activity for Side-Angle-Side. Then I will write a couple of simple examples on the board of proving triangles are congruent. I will work these out on my own to show the students the process I want to see from them when working these types of problems. Next, I will put a couple of more challenging problems on the board for the students to work on their own for a minute or two. I will be going around the room to check for understanding from the students. After a few minutes, I will go to the board and have some of the students help me work through the problems. The remainder of class, students will work on the homework for the day's lesson.