"square of a" is equal to the product of a and itself.
to refer to this, "square of a" or "squared a", which one is more idiomatic in the context of academic, such as a textbook?
English Language Learners Stack Exchange is a question and answer site for speakers of other languages learning English. It only takes a minute to sign up.Sign up to join this community
"Square of a" and "a squared" would be common in US English. "Squared a" carries an entirely different meaning (see below), which is why it's best to include complete sentences for the context (as comments suggest).
From the context, we know that you are using "squared" in the sense of something multiplied by itself. However, "squared" also means something else. It means to make something square or rectangular; to straighten things up. You might square up a row of books.
In US English, the phrase "a squared", assuming we know from the context that a is a variable, means a multiplied by itself. With "squared a", we see "a" as the indefinite article. The question is, "squared a what?" We would expect something like "squared a book on the desk", which has nothing to do with multiplying by itself.