Q:

Finding the other 2 coordinates of a rectangle if you only have 2

Is there a formula/calculation to work out how to find the other $2$ coordinates for a rectangle if you only have the bottom left and top right coordinates?
e.g. My bottom-left coordinate would be $(-1, 0)$ and top right would be $(3, -2)$, I can work out the midpoint but I can't seem to get my head around how to work out the other $2$ coordinates?

A:

Let's observe picture below. Each point $(x,y)$  of the circle that satisfy following equality can be vertice point of the rectangle :
$\left(\sqrt{(x_A-x)^2+(y_A-y)^2}\right)^2 + \left(\sqrt{(x_C-x)^2+(y_C-y)^2}\right)^2=\left(\sqrt{(x_A-x_C)^2+(y_A-y_C)^2}\right)^2$ , 
where $A(-1,0)$ , and $C(3,-2)$ are given vertices.
For example if you choose point $B_1$ you can calculate coordinates of $D_1$ by using equalities :
$x_{D_1}=2x_O-x_{B_1}$ , and $y_{D_1}=2x_O-y_{B_1}$
Answer to sub question :
If you have length of one edge , let's say $|\bar{AB_1}|$ then you can write an extra equality : 
$ |\bar{AB_1}|= \sqrt{(x_A - x)^2+(y_A-y)^2}$ , and find relation between $x$ and $y$ coordinates.

