Question

The city of St. Louis was settled by the

French in the mid 1700s and joined the
United States in 1803 as part of the
Louisiana Purchase. The city flag reflects its
French history by featuring the fleur-de-lis.
How can you prove that the left and right
petals are congruent to each other?

Answer 1

Fold it in half along a vertical line between the tip of the top and the tip of the bottom. That will lay the "petal" of one side over the "petal" of the other side, and if you can see through the flag (or the paper), you'll see that they match exactly.

Explanation:

That's called a reflection about the vertical axis.