Let \( u(x, t) \) be the solution of the initial value problem
\[
\frac{\partial u}{\partial t} + 3 \frac{\partial u}{\partial x} = u, \quad x \in \mathbb{R}, \quad t>0, \quad u(x, 0) = \cos x,
\]
and let \( v(x, t) \) be the solution of the initial value problem
\[
\frac{\partial v}{\partial t} + 3 \frac{\partial v}{\partial x} = v^2, \quad x \in \mathbb{R}, \quad t>0, \quad v(x, 0) = \cos x.
\]
Then, which of the following is/are TRUE?