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## Homework Statement

Let [tex]f (x, y) = e^x^2 + 3e^y[/tex] . At the point (0, 1) find:

(a) a vector u such that the directional derivative [tex]D_u f[/tex] is maximum and write down this maximum value,

(b) a vector v such that [tex]D_v f = 0[/tex]

## Homework Equations

grad f / directional derivative formula

## The Attempt at a Solution

I can find part (a), simply calculate the gradient vector, but part (b) I don't know what to do. The answer given is:

(b) Dv f is zero when v is tangent to the level curve passing through (0, 1), i.e. when v = i

(or some multiple of this).

I don't understand what this means.

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