← Multivariable Calculus

How to solve

D_u f = ∇f · u for a unit vector u.

Steps

  1. Compute ∇f.
  2. Dot with u.

Example

f=x²+y² at (1,2), u=⟨1,0⟩

  1. ∇f=⟨2,4⟩.
  2. Dot ⟨1,0⟩ = 2.

Answer: 2

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