The points (0, k), (0,-k), (k, 0)(0,k),(0,−k),(k,0), and (-k, 0)(−k,0), where k=/=0, comprise the vertices of a square. What is the area of the square?

The answer key says it’s 2k^{2}, but my calculations show it’s 4k^{2}. Each side is length 2k so it would be (2k)^{2} which is 4k^{2}