How to find the directional derivative of at the point (-1, -4) in the direction ? i already find the gradient of f at (-1,-4) = 160i+50j , but how can i find the directional derivative using ?
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Originally Posted by iwonder How to find the directional derivative of at the point (-1, -4) in the direction ? i already find the gradient of f at (-1,-4) = 160i+50j , but how can i find the directional derivative using ? The directional derivative in the direction of a unit vector $\displaystyle \hat{{\bf{u}}}$ is the dot product of the gradient and the unit vector. So now find the unit vector in the required direction. CB
i understand i have to find the unit vector, but how can i find at ?
Originally Posted by iwonder i understand i have to find the unit vector, but how can i find at ? Draw a picture and look at the right triangle formed. The unit vector at angle theta to the x-axis is < cos(theta), sin(theta)>.
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