If given only:
f(5,2) = 80
fx(5,2) = 8
fy(5,2) = -6
Suppose 80 is measured in degrees Fahrenheit. Find the direction where the temperature would get cooler.
I just did 8a - 6b = 0 (since using the dot product, <8,-6> * <a,b> = 0.
Then I solved for a, b, and this was the vector equation.
Then...