Subject Area Lessons

## #3749. Properties of Triangles

Mathematics, level: Senior
Posted Sun Apr 23 11:10:35 PDT 2006 by Victor Morgan (vrm5@columbia.edu).
Interactive Exploration of Triangle
New York, NY
Materials Required: computer with internet access
Activity Time: 20-25 minutes
Concepts Taught: Relationship between size of angles and sides

Step 1) Gather information from students. Take a "yes" no "vote"
ASK: "Is there any relationship between how big a side of a triangle is and how big its opposite angle is?"

Step 2) Write down poll of the votes on board.

Step 3) Now, it's time for the students to learn the answer to the poll through exploration of an interactive triangle at the following webpage www.mathwarehouse.com/geometry/triangles/interactive-triangle.htm

Step 4)After going to the web page, students should create several different triangles by moving the vertices around and creating different lengths and angles at the above web page (It's an easy to use interactive web page. Click on "directions" button if confused).

Step 5) Each time the students create a new triangle, they should record the measurments of the sides and the opposite angles and answer the following questions:

Step 6) Students should then indicate whether each side and its opposite angle are the largest, smallest or in the middle by going through these questions:

Question 1) The smallest side of this triangle is opposite _____________angle.

Question 2) The largest side of this triangle is opposite _____________angle.

Question 3) The middle-sized side of this triangle is opposite _____________angle.

Step 7) PUT THE PATTERN TOGETHER: after creating all the triangles and filling out the worksheet. Students should be able to answer the three following questions
Question 1) The smallest side of a triangle is always opposite _____________angle.

Question 2) The largest side of a triangle is always opposite _____________angle.

Question 3) The middle-sized side of a triangle is always opposite _____________angle.

Step 8) CONCLUSION: Students should now be able to answer the following summary question: What is the relationship between the size of a triangle's side and the size of that side's opposite angle?