a) x² - 4x + 3
= x² - 3x - x + 3
= ( x² - 3x ) - ( x - 3 )
= x( x - 3 ) - 1( x - 3 )
= ( x - 1 )( x - 3 )
b) x² - 5xy + 4y²
= x² - xy - 4xy + 4y²
= ( x² - xy ) - ( 4xy - 4y² )
= x( x - y ) - 4y( x - y )
= ( x - y )( x - 4y )
c) x² + 5x + 6
= x² + 2x + 3x + 6
= ( x² + 2x ) + ( 3x + 6 )
= x( x + 2 ) + 3( x + 2 )
= ( x + 2 )( x + 3 )
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