Find a normal vector to the level surface x2+y2−z=4x^2 + y^2 - z = 4x2+y2−z=4 at the point (2,1,1)(2, 1, 1)(2,1,1).
⟨4,2,−1⟩\langle 4, 2, -1 \rangle⟨4,2,−1⟩
⟨2,1,−1⟩\langle 2, 1, -1 \rangle⟨2,1,−1⟩
⟨4,2,1⟩\langle 4, 2, 1 \rangle⟨4,2,1⟩
⟨1,1,−1⟩\langle 1, 1, -1 \rangle⟨1,1,−1⟩