TL:
$a) x^3 - 3x^2 + 1 - 3x = x^2 ( 1 - 3x ) + ( 1 - 3 ) = ( 1 - 3x ) ( x^2 + 1 )$
$b) ( x^2 - 1^2 )^2 - 4a^2 = ( a^2 + 1 )^2 - 4a^2 = ( 1-a^2) ( 3a^2 + 1 )$
$c) x^3 - 3x^2 - 4x + 12 = x^2 ( x - 3 ) - 4 ( x - 3 ) = ( x - 2 )( x + 2 )(x - 3 )$
$d) x( x + y ) - 5x - 5y = x (x + y ) - 5 (x + y) = (x + y)(x - 5)$
$e) x^2 - y^2 -2xy + y^2 = x^2 - 2xy + y^2 - y^2$
$= ( x - y )^2 - y^2 = ( x - y - y ) ( x - y + y ) = x(x-2y)$
$ f) x^2 - y^2 + 4 - 4x = ( x^2 - 4x + 4 ) - y^2 = ( x - y -2 ) ( x + y - 2 ) $