A rectangle has two lines of symmetry. It can be folded horizontally and vertically, from the middle of the sides, but it cannot be folded corner to corner to achieve a line of symmetry.
A square, on the other hand, has four lines of symmetry. It can be folded in the same way as a rectangle to achieve symmetry, and it can also be folded corner to corner for lines of symmetry. An equilateral triangle has a single line of symmetry, and other triangles, such as the scalene triangle, do not have any lines of symmetry. To test a shape for lines of symmetry, fold the shape along the middle in different directions to see where the sides and corners line up perfectly.