a)
[tex](a + 4b)(2a + 1) = 2 {a}^{2} + a + 8ab + 4b[/tex]
b)
[tex] \frac{3a \times (a + 2b)}{2} = \frac{3 {a}^{2} + 6ab }{2} = 1.5 {a}^{2} + 3ab[/tex]
c)
[tex](2a - b)(3 - a) = 6a - 2 {a}^{2} - 3b + ab[/tex]
d)
[tex] \frac{(a + a + b) \times( a + 2)}{2} = \frac{(2a + b) \times (a + 2)}{2} = \frac{2 {a}^{2} + 4a + ab + 2b }{2} = {a}^{2} + 2a + \frac{1}{2} ab + b[/tex]
