https://mathproblems123.wordpress.com/2 ... -polygons/

I am trying to substitute in f(x,y)=(O+Xx+Yy-Q)² for function in that and get just a sum, complex though it will be, how do I do that with |P|=... part has dt(y...) one thing and all part of differentiation? Does it help that all but x and y may be constants and this is one of 3 like different constants for each of 3 but this is base case of 1 dimension of 3? Can you email maybejosiah@aol.com if you have a solution for this skew differentiation or a resource?