`\text{Đáp án: + Giải thích các bước giải:}`
`a ) ( x + 2 ) ( x - 5 ) = 0`
`⇔` \(\left[ \begin{array}{l}x+2=0\\x-5=0\end{array} \right.\)
`⇔` \(\left[ \begin{array}{l}x=-2\\x=5\end{array} \right.\)
`\text{Vậy S = { -2 ; 5}}`
`b ) (3x - 2)(4x + 5)=0`
`⇔` \(\left[ \begin{array}{l}3x-2=0\\4x + 5=0\end{array} \right.\)
`⇔` \(\left[ \begin{array}{l}3x=2\\4x=-5\end{array} \right.\)
`⇔` \(\left[ \begin{array}{l}x=\frac{2}{3}\\x=\frac{-5}{4}\end{array} \right.\)
`\text{Vậy S =}` `{ 2/3 ; (-5)/4 }`
`c ) ( 4x + 2 )( x^2 + 1 ) = 0`
`⇔` \(\left[ \begin{array}{l}4x+2=0\\x(x+1)=0\end{array} \right.\)
`⇔` \(\left[ \begin{array}{l}4x=-2\\x=0\\x +1=0\end{array} \right.\)
`⇔` \(\left[ \begin{array}{l}x=\frac{-1}{4}\\x=0\\x=-1\end{array} \right.\)
`\text{Vậy S =}` `{(-1)/4 ; -1;0}`
`d ) (x + 3)(2x - 5)=0`
`⇔` \(\left[ \begin{array}{l}x+3=0\\2x-5=0\end{array} \right.\)
`⇔` \(\left[ \begin{array}{l}x=-3\\x=\frac{5}{2}\end{array} \right.\)
`\text{Vậy S =}` `{-3;5/2}`
