`a)7x^2+2x=0`
`<=>x(7x+2)=0`
`<=>`\(\left[ \begin{array}{l}x=0\\7x+2=0\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=0\\7x=-2\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=0\\x=-\dfrac{2}{7}\end{array} \right.\)
Vậy `S={0;-2/7}`
`b)x(x+4)-x^2-6x=10`
`<=>x^2+4x-x^2-6x=10`
`<=>-2x=10`
`<=>x=-5`
Vậy `S={-5}`
`c)x(x-1)+2x-2=0`
`<=>x(x-1)+2(x-1)=0`
`<=>(x-1)(x+2)=0`
`<=>`\(\left[ \begin{array}{l}x-1=0\\x+2=0\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=1\\x=-2\end{array} \right.\)
Vậy `S={1;-2}`
`d)(3x-1)^2-(x+5)^2=0`
`<=>[3x-1-(x+5)](3x-1+x+5)=0`
`<=>(3x-1-x-5)(3x-1+x+5)=0`
`<=>(2x-6)(4x+4)=0`
`<=>`\(\left[ \begin{array}{l}2x-6=0\\4x+4=0\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}2x=6\\4x=-4\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=3\\x=-1\end{array} \right.\)
Vậy `S={3;-1}.`
