Lesson 11What Is the Same?
Learning Goal
Let’s decide whether shapes are the same.
Learning Targets
I can decide visually whether or not two figures are congruent.
Lesson Terms
- congruent
Warm Up: Find the Right Hands
Problem 1
A person’s hands are mirror images of each other. In the diagram, a left hand is labeled. Shade all of the right hands.
Activity 1: Are They the Same?
Problem 1
For each pair of shapes, decide whether or not they are the same.
Activity 2: Area, Perimeter, and Congruence
Problem 1
Which of these rectangles have the same area as Rectangle
but different perimeter? Which rectangles have the same perimeter as Rectangle
but different area? Which have the same area and the same perimeter as Rectangle
? Use materials from the geometry tool kit to decide which rectangles are congruent. Shade congruent rectangles with the same color.
Are you ready for more?
Problem 1
In square
Lesson Summary
Congruent is a new term for an idea we have already been using. We say that two figures are congruent if one can be lined up exactly with the other by a sequence of rigid transformations. For example, triangle
Here are some other facts about congruent figures:
We don’t need to check all the measurements to prove two figures are congruent; we just have to find a sequence of rigid transformations that match up the figures.
A figure that looks like a mirror image of another figure can be congruent to it. This means there must be a reflection in the sequence of transformations that matches up the figures.
Since two congruent polygons have the same area and the same perimeter, one way to show that two polygons are not congruent is to show that they have a different perimeter or area.