Bài 1/
$x^2-25y^2-4x+4$
$=(x^2-4x+4)-(5y)^2$
$=(x-2)^2-(5y)^2$
$=(x-2-5y)(x-2+5y)$
Bài 2/
$2x(x-1)+3x-3=0$
$\to 2x(x-1)+3(x-1)=0$
$\to (2x+3)(x-1)=0$
\(\to\left[ \begin{array}{l}2x+3=0\\x-1=0\end{array} \right.\) \(\to\left[ \begin{array}{l}2x=-3\\x=1\end{array} \right.\) \(\to\left[ \begin{array}{l}x=-\dfrac{3}{2}\\x=1\end{array} \right.\)
Bài 3/
a) $(x-4)^2+2x(3x+5)$
$=x^2-8x+16+6x^2+10x$
$=(x^2+6x^2)+(-8x+10x)+16$
$=7x^2+2x+16$
b) $(2+5x)^2-10x(3x+2)$
$=4+20x+25x^2-30x^2-20x$
$=(25x^2-30x^2)+(20x-20x)+4$
$=-5x^2+4$