+) `3x + (2x-28)=-13`
`<=> 3x+2x-28=-13`
`<=> 5x=15`
`<=> x=3`
Vậy `x=3`
+) `(x^2 +1)(x-2)=0`
`<=>` \(\left[ \begin{array}{l}x^2+1=0\\x-2=0\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}x^2=-1(vô lí)\\x=2\end{array} \right.\)
Vậy `x=2`
+) `(x-1)(x^2-4)=0`
`<=>` \(\left[ \begin{array}{l}x-1=0\\x^2-4=0\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}x=1\\x^2=4\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}x=1\\x=±2\end{array} \right.\)
Vậy `x=1 ; x=2` hoặc `x=-2`