Introduction
Triangles are polygons with the least number of sides possible. However when you put many triangles together, you can build amazing things. Think about the bridge above. How many triangles do you see? Do you see any that have the same size and shape? Do you see any transformations?
Go to GeoGebra: ACCESS - Triangles with Two Equal Sides. Complete the activity. What can you say about triangles that have two equal sides. Are they always the same shape? What else must be equal for them to be equal?
Following successful completion of this lesson, students will be able to...
- Prove two triangles are congruent using SSS and SAS
- Identify and use rigid motions to prove two triangles are congruent
Essential Questions
- What are the differences between isosceles, scalene, and equilateral triangles?
- What are the differences between acute, right, and obtuse triangles?
- How do you find the perimeter and area of a triangle in the coordinate plane?
- What information is needed to show that two triangles are congruent?
- What information is needed to show that two figures are congruent?
Enduring Understandings
- The symmetry of polygons can be described in rotations and reflections.
- The sum of the interior angles of any triangle is a constant.
- The perimeter and area of a polygon can be calculated using its x and y coordinates.
- Congruence can be used to prove theorems about triangles.
The above objectives correspond with the Alabama Course of Study: Geometry standard: 25a, 25b, and 31b.