`a)5x.(x-3)-x+3=0`
`=>5x.(x-3)-(x-3)=0`
`=>(x-3).(5x-1)=0`
`=>` \(\left[ \begin{array}{l}x-3=0\\5x-1=0\end{array} \right.\) `=>` \(\left[ \begin{array}{l}x=3\\x=\dfrac{1}{5}\end{array} \right.\)
`b)9x²-25-x.(3x+5)=0`
`=>9x²-25-(3x^2+5x)=0`
`=>9x²-25-3x²-5x=0`
`=>6x²-25-5x=0`
`=>6x²-5x-25=0`
`=>` \(\left[ \begin{array}{l}x=\dfrac{5+-25}{2.6}\\x=\dfrac{5+-25}{12}\end{array} \right.\)
`=>` \(\left[ \begin{array}{l}x=\dfrac{5}{3}\\x=-\dfrac{5}{3}\end{array} \right.\)
