# Directional Derivative

1. Jun 7, 2010

### karens

nvmnd - solved

Last edited: Jun 7, 2010
2. Jun 7, 2010

### Coto

Hey karens,

Well you have the formula written above. Why don't you start by showing us what $$f_x (2,1), f_y (2,1)$$ are and what $$a, b$$ should be considering your unit vector $$\left(\frac{3}{5}, \frac{-4}{5}\right)$$.