Bài 1:
a, $25x²+4y²-20xy$
$=(5x-2y)²$
b, $x³+6x²+12x+8$
$=(x+2)³$
Baì 2:
a, $x²-14x+49-4y²$
$=(x-7)²-4y²$
$=(x-7-2y)(x-7+2y)$
b, $9-x²+2xy-2y²$
Bài 3:
a, $x²-4x=0$
$⇔x(x-4)=0$
$⇔\left[ \begin{array}{l}x=0\\x=4\end{array} \right.$
b, $5x(x-2)-(2-x)=0$
$⇔5x(x-2)+(x-2)=0$
$⇔(x-2)(5x+1)=0$
$⇔\left[ \begin{array}{l}x=2\\x=-1/5\end{array} \right.$
c, $(x-2)²-16=0$
$⇔(x+2)(x-6)=0$
$⇔\left[ \begin{array}{l}x=-2\\x=6\end{array} \right.$