a,5x(4x-3)+6-8x=0
=>5x(4x-3)-8x+6=0
=>5x(4x-3)-2(4x-3)=0
=>(5x-2)(4x-3)=0
=>\(\orbr{\begin{cases}5x-2=0\\4x-3=0\end{cases}\Rightarrow\orbr{\begin{cases}x=\frac{2}{5}\\x=\frac{3}{4}\end{cases}}}\)
b, 5x(x-9)-x+9=0
=>5x(x-9)-(x-9)=0
=>(5x-1)(x-9)=0
=>\(\orbr{\begin{cases}5x-1=0\\x-9=0\end{cases}\Rightarrow\orbr{\begin{cases}x=\frac{1}{5}\\x=9\end{cases}}}\)