a) x² - 3 x - 4 = x² + x - 4 x - 4 = x ( x + 1 ) - 4 ( x + 1 ) = ( x + 1 ) ( x - 4 )
b) x² + 2 x - 3 = x² + 3 x - x - 3 = x ( x - 1 ) + 3 ( x - 1 ) = ( x - 1 ) ( x + 3 )
c) x² - x - 2 = x² + x - 2 x - 2 = x ( x + 1 ) - 2 ( x + 1 ) = ( x + 1 ) ( x - 2 )
d) x² + x - 6 = x² + x - 4 - 2 = x² - 4 + x - 2 = ( x - 2 ) ( x + 2 ) + ( x - 2) =
( x - 2) ( x + 2 + 1) = ( x - 2 ) ( x + 3)