Solution
= Solution
The <vorticity> points normally to the plane and has scalar component
$$
\boxed{\omega_z=v_x-u_y=2\sin x\cos y=2\psi}.
$$
It is nonzero in general, so the flow is rotational.
= Solution
The <vorticity> points normally to the plane and has scalar component
$$
\boxed{\omega_z=v_x-u_y=2\sin x\cos y=2\psi}.
$$
It is nonzero in general, so the flow is rotational.