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By Freya Edholm
A square has 4 lines of symmetry: the diagonals and the line segments connecting the opposite midpoints of each side. So if one was to fold a square in half to make 2 rectangles, or 2 45-45-90 triangles, those would be lines of symmetry. This is so because the two rectangles created are both x by 2x rectangles, where x is the side length of the square. Also the 45-45-90 triangles are congruent because of the ASA postulate (they share a side).