If the unit vector u makes an angle theta with the positive x axis then we can write u = <cos theta, sin theta>(adsbygoogle = window.adsbygoogle || []).push({});

D_{u}f(x, y) = f_{x}(x,y) cos theta + f_{y}(x,y) sin theta

What if I am dealing with a function with three variables (x, y, z)?

How can I find the directional derivative if I have been given an angle?

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# Directional derivatives and the gradient vector

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