Phenomena manifest in many ways, many perspectives.
The colour "red" is a human phenomena, and the notion of "wavelengths" and "energy" are also something humans see/have/experience as phenomena. You can then use signifiers, signified, words, sounds, etc. to say "red" for what you see in your vision as "red" whilst noting on some instrument the "wavelength".
There is no really real reality beyond your experience of sights, sounds, concepts, etc. -- reality which we can speak of, IF we can't observe it. In this sense, you don't create reality, but likewise, hallucinations are "real" for you. There is basically no firm ground to stand on, hence phenomena are "empty". But that doesn't mean YOU are creating "reality", what you are is a phenomena experiencing machine, which has a set of senses. The point is, we can't ask is the equation "real", because we can't access the truly real reality directly anyway. Whatever the "sun" is, we know it rises and sets, as experienced by all human beings and animals. Your sight of the sun is as real as the mathematical formula describing its motion and vice versa.
Whether you're experiencing a mathematical abstract idea or a colour in your vision, that's what you have and it is co-created perception, just like you need a lens to focus light. That doesn't mean we create reality, rather we create our dream implicitly by being an instrument which can experience.
It is a lot easier if you think of the mind as just another sense organ. So sight is a sense organ, and mathematics is a sense organ. Thoughts are a sense organ. Just because you see red doesn't mean reality is made of redness. Your senses manifest that particular representation/perspective.
What I think most people mean by "reality" in the everyday sense of the word is that this stuff over here correlates with that stuff over there. A real car correlates with death if you stand in the middle of the road. A hallucinatory car (which looks as real as the real one) doesn't. Your math equation is "real" if it correlates with the stuff you're modelling.
So to try to answer the question, the math equation is "created" in the sense that a human thought of it, but it is no more separate from reality than the phenomena you're trying to study, because that phenomena is itself something your perceptual senses are "creating" also. We never see the really real directly. Seeing is an activity. Not that it makes much difference. Trouble is we are sentient and so sentience is always part of whatever it is you're "seeing out there".