Which vector field is conservative?
⟨y,x⟩\langle y, x \rangle⟨y,x⟩
⟨−y,x⟩\langle -y, x \rangle⟨−y,x⟩
⟨y,−x⟩\langle y, -x \rangle⟨y,−x⟩
⟨x,−y⟩\langle x, -y \rangle⟨x,−y⟩