If \( \theta_1 \) and \( \theta_2 \) are the values of \( \theta \in (0,\pi) \) for which the system of linear equations
\[
x+3y+7z=0,
\]
\[
-x+4y+7z=0,
\]
\[
(\sin 3\theta)x+(\cos 2\theta)y+2z=0
\]
has a non-trivial solution, then \( |\theta_1-\theta_2| \) is equal to