\(a.\)
\(5x\left(4x-3\right)+6-8x=0\)
\(\Rightarrow5x\left(4x-3\right)-2\left(4x-3\right)=0\)
\(\Rightarrow\left(5x-2\right)\left(4x-3\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}5x-2=0\\4x-3=0\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=\dfrac{2}{5}\\x=\dfrac{3}{4}\end{matrix}\right.\)
Vậy : ==-.
\(b.\)
\(5x\left(x-9\right)-x+9=0\)
\(\Rightarrow5x\left(x-9\right)-\left(x-9\right)=0\)
\(\Rightarrow\left(5x-1\right)\left(x-9\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}5x-1=0\\x-9=0\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=\dfrac{1}{5}\\x=9\end{matrix}\right.\)
Vậy : ==