OK, I having a small problem understanding how my text book came about an answer to an example problem.(adsbygoogle = window.adsbygoogle || []).push({});

[tex]f(x,y)=4-x^2-\frac{1}{4}y^2[/tex]

at P(1,2)

This next step is the one that's bugging me:

[tex]u^\rightarrow=\cos(\frac{\pi}{3})\imath+\sin(\frac{\pi}{3})\jmath[/tex]

This is one of those instances where something magic happens because right now I have little to no clue where the [tex]\frac{\pi}{3}[/tex] came from.

Thanks...

**Physics Forums | Science Articles, Homework Help, Discussion**

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Directiontal derivative

**Physics Forums | Science Articles, Homework Help, Discussion**