a ) x² + 3 x + 2 = x² + x + 2 x + 2 = x ( x + 1 ) + 2 ( x + 1 ) = ( x + 1 ) ( x + 2 )
b ) x² + 6 x + 5 = x² + x + 5 x + 5 = x ( x + 1 ) + 5 ( x + 1 ) = ( x + 1 ) ( x + 5 )
c ) x² + 8 x + 15 = x² + 3 x + 5 x + 15 = x ( x + 3 ) + 5 ( x + 3 ) = ( x + 3 ) ( x + 5 )
d ) x² + 7 x + 12 = x² + 3 x + 4 x + 12 = x ( x + 3 ) + 4 ( x + 3 ) = ( x + 3 ) ( x + 4 )