Geometric Demonstrations Are Grounding in the Spaces

The idea is that when we have knowledge of things, we're in the realm of ideas. It's not like we get a bunch of sensory stimuli and then we act the generalities from them. Rather, we're directly in touch with this kind of formal realm all by ourselves. So where do we get the truth of aplus b squared equals a squared pus b squared pus to a b? Where does that come from? Not from the senses, but from that reasonable realm of extension - even if we get at it by using our senses.