a=(x-3) (x+2)

=x²+2x-3x-6

=x²-x-6

b= (y+2) (y-3)

=y²-3y+2y-6

=y²-y-6

 c=(4x+1) (5-x)

=20x-4x²+5-x

=-4x²+19x+5

d= (5y-2) (y+3)

=5y²+15y-2y-6

=5y²+13y-6

a = x² + 2x - 3x -6

a = x² -x -6

b = y² - 3y + 2y -6

b = y² -y -6

c = 20x -4x² +5 - x

c = 4x² -19x +5

d = 5y² +15y -2y -6

d = 5y² +13 y -6

voilà voilà ;)