Folding Test. You can find if a shape has a Line of Symmetry by folding it. When the folded part sits perfectly on top (all edges matching), then the fold line is a Line of Symmetry. Here I have folded a rectangle one way, and it didn't work. So this is not a Line of Symmetry. But when I try it this way, it does work (the folded part sits perfectly on top, all edges matching): So this is a Line of Symmetry. Triangles A Triangle can have 3, or 1 or no lines of symmetry: