b, -5x² + 6x - 1
= -5x² + 5x + x - 1
= -( 5x² - 5x ) + ( x - 1 )
= -5x( x - 1 ) + ( x - 1 )
= ( x - 1 )( -5x + 1 ).
c, x² - 9 - 6y - 2xy
= ( x² - 9 ) - ( 2xy + 6y )
= ( x² - 3² ) - 2y( x + 3 )
= ( x - 3 )( x + 3 ) - 2y( x + 3 )
= ( x + 3 )( x - 3 - 2y ).