x^2 -6( x-3)-9 
= x^2 -6x-18-9
= x^2 -6x -27 
= x^2 -9x +3x -27 
=x ( x-9 ) + 3 ( x-9 )
= ( x + 3 ) ( x-9 )

đến nay 2018 + 2000 = 4018 <=> 40 thế kỉ

x^2 =1/16
<=> x^ 2- 1/16= 0 
<=> ( x-1/4 ) ( x+ 1/4 ) =0 
<=> /x- 1/4 =0
       / x+1/4 =0 
<=> x= 1/4 
       x= -1/4
             

x(x-1) + y(x-1 )
= (x + y ) ( x-1)