[tex]d = 7 \ cm\\oraz\\d = a\sqrt{2}\\\\a\sqrt{2} = 7 \ \ /:\sqrt{2}\\\\a = \frac{7}{\sqrt{2}}\cdot\frac{\sqrt{2}}{\sqrt{2}} = \frac{7\sqrt{2}}{2} \ cm[/tex]
[tex]P = a^{2}\\\\P = (\frac{7\sqrt{2}}{2})^{2} = \frac{49\cdot2}{4} = \frac{49}{2} = 24,5 \ cm^{2}[/tex]
