Question

Find the directional derivative of the function at the point p in the direction given by the angle theta, measured from the positive direction of the x-axis in the counterclockwise direction: f(x,y)= cos(2x+y) p=(6,-1) and theta=-pi/3

Answer 1

So I found the gradient of f at the point (6,-1): (-2sin(11), -sin(11)) but I'm thrown off by the angle theta. Normally to find the directional derivative, I'd dot product the gradient of the function f at a point with a unit vector.

Answer 2

My work so far: