Solution
= Solution
For the printed <coefficients>, $p=2\sin x\cosh y$ and $q=\sin^2x\sinh y$. Their cross <derivatives> are
$$
p_y=2\sin x\sinh y,\qquad q_x=2\sin x\cos x\sinh y.
$$
They are not equal as <functions>; their difference is $2\sin x(1-\cos x)\sinh y$. Hence \b[the form is not exact]. Agreement on certain <lines> or isolated points is insufficient, because exactness requires the <derivative> identity throughout an open domain.