Investigate some necessary conditions for creating a triangle.

• Students will recognize that the largest angle in a triangle is opposite the largest side, the second largest angle is opposite the second largest side, and the smallest angle is opposite the smallest side.
• Students will recognize that given three segments and three angles that form a triangle, the triangle will be unique.

• opposite sides
• opposite angles

This lesson involves students manipulating three segments and three angles to build a triangle. As a result students will:

• Attach an angle to the longest segment; discover that the largest angle cannot be attached to the longest side to form a triangle.
• Build a triangle starting with the largest angle; discover there are restrictions on which side has to be opposite which angle.
• Recognize and generalize the relationship between the sides and the angles in a triangle.