a) `5x(x-1)=x-1`
`⇒ 5x(x-1)-(x+1)=0`
`⇒ (5x-1)(x-1)=0`
`⇒` \(\left[ \begin{array}{l}5x-1=0\\x-1=0\end{array} \right.\)
`⇒` \(\left[ \begin{array}{l}5x=1\\x=1\end{array} \right.\)
`⇒` \(\left[ \begin{array}{l}x=1/5\\x=1\end{array} \right.\)
b) `2(x+5)-x²-5x=0`
`⇒ 2(x+5)-(x²+5x)=0`
`⇒ 2(x+5)-x(x+5)=0`
`⇒ (2-x)(x+5)=0`
`⇒` \(\left[ \begin{array}{l}2-x=0\\x+5=0\end{array} \right.\)
`⇒` \(\left[ \begin{array}{l}x=2\\x=-5\end{array} \right.\)
