\(f\left(x\right)=3sin\left(2x-\dfrac{\pi}{4}\right)-4\)
\(\Leftrightarrow-1\le2x-\dfrac{\pi}{4}\le1\)
\(\Leftrightarrow-3\le3sin\left(2x-\dfrac{\pi}{4}\right)\le3\)
\(\Leftrightarrow-7\le3sin\left(2x-\dfrac{\pi}{4}\right)\le-1\)
Vậy \(Min=-7\), \(Max=-1\).