a)
[tex] \frac{2 \times 2}{2} = 2 {dm}^{2} [/tex]
[tex] \frac{2 \times 3}{2} = 3 {dm}^{2} [/tex]
[tex] \frac{2 \times 4}{2} = 4 {dm}^{2} [/tex]
Czyli
[tex]2 + 3 + 4 = 9 {dm}^{2} [/tex]
b)
[tex]4( \frac{5 \times 10}{2} ) = 4( \frac{50}{2} ) = 4 \times 25 = 100 {cm}^{2} [/tex]
