[tex]a=H[/tex]
[tex]h=5[/tex]
[tex]h=a\sqrt{2}\\a\sqrt{2}=5\quad|:\sqrt{2}\\a=\dfrac{5}{\sqrt{2}}\cdot\dfrac{\sqrt{2}}{\sqrt{2}}\\a=\dfrac{5\sqrt{2}}{2}[/tex]
[tex]P_b=4P_\Delta[/tex]
[tex]P_\Delta=\dfrac{ah}{2}\\P_\Delta=\dfrac{\dfrac{5\sqrt{2}}{2}\cdot5}{2}=\dfrac{25\sqrt{2}}{2}:2=\dfrac{25\sqrt{2}}{2}\cdot\dfrac{1}{2}=\dfrac{25\sqrt{2}}{4}[/tex]
[tex]P_b=4\cdot\dfrac{25\sqrt{2}}{4}=25\sqrt{2}[/tex]
