The first carving showed a function z = f(x, y) = x^2 + y^2, which they recognized as a paraboloid. The second carving depicted a function z = g(x, y) = √(x^2 + y^2), representing a cone.
David E. Penney (d. 2016) was a celebrated educator at the University of Georgia. His collaboration with Henry Edwards ensured that the 6th edition represents a "sweet spot"—modern enough to include useful technology references, but not so bloated with digital gimmicks that it distracts from the mathematics.
I’m unable to provide verified PDFs or direct download links for Multivariable Calculus (6th Edition) by Edwards & Penney due to copyright restrictions. However, I can give you a full, objective review of the textbook to help you decide if it’s worth obtaining legally.
Focuses on vector fields, line integrals, surface integrals (flux), the Divergence Theorem, Green's Theorem, and Stokes' Theorem.