Đáp án:
`c//` \(\left[ \begin{array}{l}x=-\sqrt7\\x=\sqrt7\end{array} \right.\) \(\left[ \begin{array}{l}x=-\sqrt7\\x=\sqrt7\end{array} \right.\)
`d//` vô nghiệm
`e//` `x \in {0;2;-2}`
`g//` \(\left[ \begin{array}{l}x=3\\x=\dfrac{-1}{2}\end{array} \right.\)
`h//` `x=-1`
Giải thích các bước giải:
`c//` `x^2-7=0`
`=>` `x^2=7`
`=>` \(\left[ \begin{array}{l}x=-\sqrt7\\x=\sqrt7\end{array} \right.\)
$\\$
`d//` `x^2+4=0`
`=>` `x^2=-4`
`=>` vô nghiệm
$\\$
`e//` `x^3-4x=0`
`=>` `x . x^2-4x=0`
`=>` `x(x^2-4)=0`
`TH1:` `x=0`
`TH2:` `x^2-4=0`
`=>` `x^2=4`
`=>` `x={2;-2}`
vậy `x \in {0;2;-2}`
$\\$
`g//` `2x^2-5x-3=0`
`=>` `2x^2-(6x-x)-3=0`
`=>` `2x^2-6x+x-3=0`
`=>` `2x^2-2x3+x-3=0`
`=>` `2x(x-3)+1(x-3)=0`
`=>` `(2x+1)(x-3)=0`
`=>` \(\left[ \begin{array}{l}x-3=0\\2x+1=0\end{array} \right.\) `<=>` \(\left[ \begin{array}{l}x=3\\x=\dfrac{-1}{2}\end{array} \right.\)
$\\$
`h//` `x^3+x^2+2x+2=0`
`=>` `x^2(x+1)+2(x+1)=0`
`=>` `(x^2+2)(x+1)=0`
`=>` \(\left[ \begin{array}{l}x^2+2=0\\x+1=0\end{array} \right.\) `<=>` \(\left[ \begin{array}{l}x^2=-2(KTM)\\x=-1\end{array} \right.\)
