a)
(x + 4) * (x - 3) =
= x² - 3x + 4x - 12 = x² + x - 12
b)
(2a + 1) * (b - 6) =
= 2ab - 12a + b - 6
c)
(5x + y) * (x + 2y) =
= 5x² + 10xy + xy + 2y² =
= 5x² + 2y² + 11xy
d)
(3x + 2y) * (x + 2y + 3) =
= 3x² + 6xy + 9x + 2xy + 4y² + 6y =
= 3x² + 4y² + 8xy + 9x + 6y