Bài 1: x^2-6x+9-25y^2= (x^2-6x+9)-25y^2
=(x-3)² -(5y)²
=(x-3-5y)(x-3+5y)
Bài 2:
b) 5x ( x-3 ) - ( x-2 )^2=5x² -15x -x²+4x-4
=4x² -11x-4
c) (2x+3)^2-(2x-3)(2x+3)-7=(2x+3)(2x+3-2x+3) -7
= (2x+3)6-7
=12x+11
Bài 3:
d) (1-2x) (1+2x) -x (3-4x)=7
1-(2x)² -3x+4x² =7
-3x=6
x=-2
e) x^2-9+2 (x+3)=0
x² -9+2x+6=0
x²+2x-3=0
(x-1)(x+3)=0
\(\left[ \begin{array}{l}x-1=0\\x+3=0\end{array} \right.\)
\(\left[ \begin{array}{l}x=1\\x=-3\end{array} \right.\)