What is a line of symmetry?
A line of symmetry divides a figure into two halves that are the
mirror images of each other.
Fold a square sheet of paper exactly in half. When you unfold
the paper you will see the crease down the center. That is an
example of a line of symmetry. Both sides of an object must be
equal to be symmetrical. Let's do a construction taking off on this
idea. You've probably already done it at one time or another.
Fold that piece of paper, and take a pair of scissors and cut
half a heart out of it using the crease as a line going down the
"middle" of the heart. Unfold the finished construction. You'll
have a heart and that fold you made in the paper is the line of
symmetry for the figure. The line of symmetry divides any shape
into mirror images.