Often I like to make a subject more accessible by breaking it down into more manageable chunks. Sometimes these chunks have established mathematical names. For instance, before teaching the Pythagorean theorem, I would like to investigate right triangles with a perpendicular drawn from the right angle vertex to the hypotenuse. The geometric mean of two numbers appears again and again in such calculations. I think it is worthwhile to introduce the term “geometric mean” at this point. This prepares students beautifully for understanding the Pythagorean theorem – you can have them “solving” right triangles using similarity before they have seen the theorem, and the theorem follows by just doing the same stuff to a general triangle.
The concept of “geometric mean” is not in the standards, but I believe that it is of great utility in getting students to develop an appreciation for the Pythagorean theorem. Is it “Common core aligned” to introduce this operation? More generally, if a concept of great utility connects to a standard, but is not explicitly mentioned, may it be included in “Common core aligned” material?