If it is a rhombus then you know each side is the same length, so only have to work out one side. To do this you have to use Pythagoras' theorem (a^2 + b^2 = c^2) So take two sets of coordinates, for example, (0,3) and (5,3), a and b represent the height difference and the length difference. Therefore (5-0)^2 + (3-3)^2 = c^2 c^2 = 25 c = 5 , which would be the side of the rhombus
