a . z ² - ( x² - 2x +1 ) = z² - ( x -1 ) ² = ( z -x +1 ) ·( z+ x -1 )
b. x² - 9 -x - 3 = ( x - 3 ) ·( x +3 ) - ( x+3 ) = ( x +3 ) · ( x -4 )
c. x² -5x + ( x -5 ) = x ( x -5 ) + ( x -5 ) = ( x -5 ) · ( x +1 )
d. ( x³ - x ² ) - 4 ( x -1 ) = x² ( x -1 ) - 4 ( x -1 ) = ( x -1 ) · ( x² - 2² ) =
= ( x -1 ) · ( x -2 ) · ( x +2 )