"These are triangles, not rectangles nor circles."
Translation:אלה משולשים, לא מלבנים ולא עיגולים.
אלו משולשים, לא מלבנים או עיגולים
Would be the correct translation, since the given translation would translate back to English as "These are triangles, not rectangles and not circles." I would argue that nor = or in Hebrew.
The word עיגול refers to the entire circle including the area inside it, while מעגל is only the outside line. But people often mix up the two. To describe the shape of a circular object such as a coin you'd use עיגול, but for people standing in a circle you'd say מעגל.