Congruent figures

Start by asking your students which shape is bigger:

Here's the answer.

Next, students will learn the etymology of the word congruent. That is, they'll see words with similar meaning and learn that congruent means same size and same shape. After that, students will learn that figures are congruent if and only if they have the same shape and size. Then students will learn that corresponding sides and angles in congruent figures are congruent.

Next, students will learn that figures are congruent if and only if there is a mapping from one to the other via a series of rigid transformations.

Finally, give your students this challenge, then this one.