[tex] \frac{(a + b) \times h}{2} [/tex]
a)
[tex] \frac{(9 +19) \times 12}{2} = \frac{28 \times 12}{2} = 14 \times 12 = {168dm}^{2} [/tex]
b)
[tex] \frac{(16 + 23) \times 20}{2} = {390cm}^{2} [/tex]
c)
[tex] \frac{(6 + 9) \times 50}{2} = {375dm}^{2} [/tex]
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