- #1
Amrator
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Homework Statement
Suppose ##D_if(P) = 2## and ##D_jf(P) = -1##. Also suppose that ##D_uf(P) = 2 \sqrt{3}## when ##u = 3^{-1/2} \hat i + 3^{-1/2} \hat j + 3^{-1/2} \hat k##. Find ##D_vf(P)## where ##v = 3^{-1/2}(\hat i + \hat j - \hat k)##.
Homework Equations
The Attempt at a Solution
$$2\sqrt{3} = ∇f ⋅ 3^{-1/2}(\hat i + \hat j - \hat k)$$
$$= 3^{-1/2}(∂f/∂x + ∂f/∂y + ∂f/∂z)$$
$$6 = (∂f/∂x + ∂f/∂y + ∂f/∂z)$$
This is where I'm stuck. I would appreciate hints.