That is the formula (comes from latin word form) of a sphere. The definition of a sphere though is a round surface such that every point on it’s surface is equidistant from its centre.
And that is precisely what the equation (or formula) says! (Well, I wrote an inequality, but never mind).
We could eliminate the term “z2” in the inequality and what remains would represent a circle. Or we could add another term, like “w2” and we would get something that we cannot imagine, but which we can conceive, and the three inequalities share the same general form:
x2 + y2 <= r2
x2 + y2 + z2 <= r2
x2 + y2 + z2 + w2 <= r2
Now, when you say that your mind holds the form of the sphere, or the form of the circle, or the form of the other mathematical entity, it is obvious to me that your mind does not become circular, or spherical or, whatever. What happens is that you establish certain variables and determine certain relations between them, and you even might realize that you can generalize those relations to use them in situations which apparently have nothing to do. A similar thing happens when you say your mind holds the form of a rock or any other object. When Mendeleev was classifying the chemical elements that he knew, he realized that there should be some other elements which he did not know yet; but he was able to predict some of their physical chemical properties. When those elements were discovered, it was shown that Mendeleev’s predictions were correct. How could that be? Because he generalized correctly some relations that he had established among the elements that he already knew.
When we say we understand, or comprehend, or have the concept of, or the idea of, or the form of something, it means that we have identified some variables among which we have established a set of relations.
Now, what is a relation? I say that it is a “conatus” whose substrate is our intellectual faculty, or our imagination, or in many instances even our body. I cannot conceive that applied to God. That is a tremendous defect compared to the notion of God as actus purus.
God is not a composite of form and matter. He doesn’t fit into any classification of existing things. As his existence is his essence. He is not a genus of anything.
I don’t know if with this you are trying to respond to my objection (“We are able to talk about God too, but it does not mean that we have the “form” of God in our minds”), but if so, I have to say it is not a proper response.
We are able to talk about God because we have established certain relations between Him and His creatures, which we call “analogies”. This is one of the principal ways in which we, as rational beings, proceed. Now, our analogies can be very poor, and I think that to attribute thoughts to God is one of those very poor analogies. It is hard to me to think that God knows by analogy.