a)
[tex] \frac{4 \times 5}{2} = \frac{20}{2} = 10 {cm}^{2} [/tex]
b)
[tex] \frac{6 \times 6}{2} = \frac{36}{2} = 18 {m}^{2} [/tex]
c)
[tex] \frac{a \times b}{2} [/tex]
d)
[tex] \frac{m \times m}{2} = \frac{ {m}^{2} }{2} [/tex]
