> Today I had a student in my college algebra class ask me why > "Quadratic Equations" are so named. If we have a polynomial of > degree 3 set equal to zero, we call it a cubic equation and that > makes sense to these students. However, this particular student is > curious because she sees "Q-U-A-D" in quadratic and thinks of four, > yet the polynomial in such an equation is only of degree 2. I've > never encountered this question before and I was at a loss for an > explanation. Does anyone know the origin of the term "quadratic > equation"? I would be very grateful to receive an answer. > > > Thank you in advance. > > Jeff Darrow > Idaho State University > > The answer is just that "quadratic" means "square", and that both these words are derived from the number (4) of sides to a square, rather from its dimension (2).
By the way, my forthcoming "Book of Numbers", written jointly with Richard Guy, contains a long discussion of many words that are related in some way to numbers, and includes the history of "square", "quadratic", and "biquadratic" (which was an old name for what is now called "quartic").