Solution
= Solution
{c}
The <vorticity> is perpendicular to the plane:
$$
\boxed{\boldsymbol\omega=(0,0,v_x-u_y)
=(0,0,2\sin x\cos y)=(0,0,2\psi).}
$$
It is generally nonzero, so this is a rotational flow even though it has a streamfunction.
= Solution
{c}
The <vorticity> is perpendicular to the plane:
$$
\boxed{\boldsymbol\omega=(0,0,v_x-u_y)
=(0,0,2\sin x\cos y)=(0,0,2\psi).}
$$
It is generally nonzero, so this is a rotational flow even though it has a streamfunction.