A few weeks ago, I ranted about the overuse of calculators in math classes, and mentioned that textbooks often ask really weird questions that seemed designed mainly to exercise your calculator fingers. I couldn’t think of any examples at the time, but today I ran across a precalculus textbook which contained the following series of questions.

In the following questions, use the determinant function on a graphing utility [read: calculator] to find a) det(A), b) det(B), c) AB, d) det(AB).

Each question consisted of two large-ish (4X4 or 5X5) matrices, namely A and B. There was no motivation for the choice of matrices, and the student wasn’t asked to do anything with the results. Leaving aside the fact that a determinant function won’t compute AB, what is the pedagogical purpose of this question? If anyone has an answer, would you please, please, please enlighten me? (By the way, if you don’t know what a determinant is, don’t worry. The math content is totally irrelevant.)

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Perhaps they’re hoping the student will then spontaneously notice that det(AB) = det(A) det(B). That seems a bit much to hope for, though.