How can i determine whether or not a polygon has symmetry?

We need to explain how can say that whether a polygon has symmetry or not.

If a line or more divides a polygon in two congruent parts such that one parts in mirror image of another part across that line, then the polygon has symmetry.

In other words, if a line is drawn on a polygon and that line divides the polygon in such a way so that If we can reflect one part of polygon over that line and the we get second part.

That line is called line of symmetry and line of reflection.

If a polygon have line of symmetry, then the polygon has symmetry.