Math. 311 Spring 2000
HOMEWORK SUMMARY REPORT
Assignment number: 4
Problem number: 3.4.9
Number of papers received: 3
Reviewing committee (Greek letter): Lambda
List all participating members: Paul McWhorter
Rich Skinner
Author[s] of paper[s] chosen for publication: [Alisa Marshall]
Comments: Good papers all around, although not everyone wrote down the
questions or had good explainations for every solution. Only one student
did part d, I guess it wasn't assigned. When it came to calculating the
directional derivative, some students used the unit direction vector,
and some only used the given direction vector. I believe the question in
the book, or the book itself may have made a poor distinction between
what vector should be used.
INSTRUCTOR'S COMMENT: I thought this distinction was already beaten to
death in Sec. 2.4. "The directional derivative in the direction of ..."
calls for the rate of change per unit displacement in that direction, so
the unit vector should be used. (Just as in one dimension, the derivative
of something is the linear approximation to the effect of a change of the
variable by one unit, no matter how large an actual change occurs in some
scenario.)