9.4: Computing partial derivatives algebraically.

Main points
The notation f_x(x, y) represents the partial derivative of the ordinary derivative of f(x, y) wrt y with x fixed and vice versa. Partial derivatives can be differentiated a second time to obtain second-order partial derivatives. A typical function such as z = f(x, y) would have 2 first-order partial derivatives and 4 second order partial derivatives.

Challenges
The book had to complicate things further just as I thought I was getting first-order partial derivatives. I understand what the entire concept is....computation is troublesome.

Reflections
Most of this is beginning to seem rather "far out there." Obviously with the examples used these actually DO have some real life applications but just how relevant is it to people who are not really concerned with how it all works.