a ) a x - b x + a y - b y = x ( a - b ) + y ( a - b ) = ( a - b ) ( x + y )
b ) ( 3 - a ) ( b - 4 ) - b + 4 = 3 b - ab - 12 + 4 a - b + 4 =
= 2 b - ab + 4 a - 8 = b ( 2 - a ) - 4 ( 2 - a ) = ( 2 - a ) ( b - 4 )
c)
x³ + x² - 9 x - 9 = x² ( x + 1 ) - 9 ( x + 1 ) = ( x + 1 ) ( x² - 9 ) = ( x + 1 ) ( x - 3 ) ( x + 3²)
d)
x² + 3 x + 2 = x² + x + 2 x + 2 = x ( x + 1 ) + 2 ( x + 1 ) = ( x + 1 ) ( x + 2 )
e)
x² + 8 x + 15 = x² + 3 x + 5 x + 15 = x ( x + 3 ) + 5 ( x + 3 ) = ( x + 3 ) ( x + 5 )
f )
x² - 7 x + 12 = x² - 3 x - 4 x + 12 = x ( x - 3 ) - 4 ( x - 3 ) = ( x - 3 ) ( x - 4 )
g )
x² + 8 x - 33 = x² + 11 x - 3 x - 33 = x ( x + 11 ) - 3 ( x + 11 ) = ( x + 11 ) ( x - 3 )