`a)`
`3-4x(25-2x)=8x^2+x-300`
`<=>3-100x+8x^2=8x^2+x-300`
`<=>8x^2-8x^2-100x-x=-300-3`
`<=>-101x=-303`
`<=>x=3`
Vậy `S={3}`
$\\$
`b)`
`x-(2x-5)/5+(x+8)/6=7+(x-1)/3`
`<=>(30x-6(2x-5)+5(x+8))/30=(7.30+10(x-1))/30`
`<=>30x-12x+30+5x+40=210+10x-10`
`<=>23x+70=10x+200`
`<=>23x-10x=200-70`
`<=>13x=130`
`<=>x=10`
Vậy `S={10}`
$\\$
`c)`
`2x(x-3)+5(x-3)=0`
`<=>(2x+5)(x-3)=0`
`<=>` \(\left[ \begin{array}{l}2x+5=0\\x-3=0\end{array} \right.\) `<=>` \(\left[ \begin{array}{l}x=-\dfrac{5}{2}\\x=3\end{array} \right.\)
Vậy `S={-5/2;3}`
$\\$
`d)`
`(x^2-4)-(x-2)(3-2x)=0`
`<=>(x-2)(x+2)-(x-2)(3-2x)=0`
`<=>(x-2)(x+2-3+2x)=0`
`<=>(x-2)(3x-1)=0`
`<=>` \(\left[ \begin{array}{l}x-2=0\\3x-1=0\end{array} \right.\) `<=>` \(\left[ \begin{array}{l}x=2\\x=\dfrac{1}{3}\end{array} \right.\)
Vậy `S={1/3;2}`
