1)
b) $14x(x-y)-21y(y-x)+28z(x-y)=14x(x-y)+21y(x-y)+28z(x-y)=7(x-y)(2x+3y+4z)$
2)
a) $9x^2-18x=0$
`<=>`$9x.x-9x.2=0$
`<=>`$9x(x-2)=0$
`<=>`\(\left[ \begin{array}{l}x=0\\x=2\end{array} \right.\)
Vậy: ...
b) $x(x-2)+5(2-x)=0$
`<=>`$x(x-2)-5(x-2)=0$
`<=>`$(x-2)(x-5)=0$
`<=>`\(\left[ \begin{array}{l}x=2\\x=5\end{array} \right.\)
Vậy: ...
d) Không chắc.
$16x^2-(3x-2)^2=0$
`<=>`$(4x)^2-(3x-2)^2=0$
`<=>`$(4x-3x-2)(4x-3x+2)=0$
`<=>`$(1x-2)(1x+2)=0$
`<=>`\(\left[ \begin{array}{l}1x-2=0\\1x+2=0\end{array} \right.\)`<=>`\(\left[ \begin{array}{l}1x=2\\1x=-2\end{array} \right.\)`<=>`\(\left[ \begin{array}{l}x=2\\x=-2\end{array} \right.\)
Vậy: ...