\(A=5a^2(1+\sqrt5+\sqrt{5+2\sqrt5})\\
A=5\cdot10^2\cdot(1+\sqrt5+\sqrt{5+2\sqrt5})\\
A=500(1+\sqrt5+\sqrt{5+2\sqrt5})\\
A\approx3157\)
\(\alpha=\dfrac{(n-2)\cdot180}{n}\\\\
\alpha=\dfrac{(20-2)\cdot180}{20}\\
\alpha=\dfrac{18\cdot180}{20}\\
\alpha=162\)
