a)
[tex]a = 9 \ cm - 2 \ cm = 7 \ cm\\h = 3 \ cm\\\\P = \frac{1}{2}ah = \frac{1}{2}\cdot7\cdot3 = \frac{21}{2} =\underline{10,5 \ cm^{2}}[/tex]
b)
[tex]a = 5 \ cm - 1 \ cm = 4 \ cm\\h = 9 \ cm\\\\P = \frac{1}{2}ah = \frac{1}{2}\cdot4\cdot9 = 2\cdot9 = \underline{18 \ cm^{2}}[/tex]
c)
[tex]a = 9 \ cm - 4 \ cm = 5 \ cm\\h = 4 \ cm\\\\P = \frac{1}{2}ah = \frac{1}{2}\cdot5\cdot4 = 5\cdot2 = \underline{10 \ cm^{2}}[/tex]
