Look at the blue line going from 00 to 30. The length of a diagonals is the distance between any pair of opposite vertices. D perimeter42 knowing square perimeter.
X Research source This method only works if you are given the perimeter of the square.
D 2area if area is given. Lets pick B and C. To find the distance between two points x 1 y 1 and x 2 y 2 all that you need to do is use the coordinates of these ordered pairs and apply the formula pictured below. In the Euclidean plane let point have Cartesian coordinates and let point have coordinates Then the distance between and is given by.