\(\left(\frac{3-2x}{\sqrt{4x-1}}\right)'=\frac{-2\sqrt{4x-1}+\frac{2\left(2x-3\right)}{\sqrt{4x-1}}}{4x-1}=\frac{-2\left(4x-1\right)+2\left(2x-3\right)}{\left(4x-1\right)\sqrt{4x-1}}\)
\(=\frac{-4x-4}{\left(4x-1\right)\sqrt{4x-1}}\Rightarrow\frac{a}{b}=-1\)