x² - 3 x - 54 = x² + 6 x - 9 x - 54 = x ( x + 6 ) - 9 ( x + 6 ) = ( x + 6 ) ( x - 9 )
x² - 18 x + 81 = ( x - 9 )²
x² + 12 x + 36 = ( x + 6 )²
... = ( x + 6 ) · ( x - 9 ) / ( x - 9 )² * ( x + 6 )² / ( x + 6 ) = ( after cancellation )
= ( x + 6 )² / ( x - 9 )
