\textbf{12.} If the figure below shows part of the graph of the function $f(x) = a + b\sin(cx - \dfrac{3\pi}{4})\cos(cx - \dfrac{3\pi}{4})$, what is the difference of the zeros of $f$ in the interval $[0, \pi]$?
\textit{[Figure: A sinusoidal curve with maximum value 3 and minimum value $-1$, with a visible point at $x = \pi$ on the x-axis]}
\begin{itemize}
\item[(1)] $\dfrac{\pi}{6}$
\item[(2)] $\dfrac{\pi}{4}$
\item[(3)] $\dfrac{\pi}{2}$
\item[(4)] $\dfrac{2\pi}{3}$
\end{itemize}