- Untitled.png (36.82 KiB) Exibido 893 vezes
[tex3]\begin{cases}\delta=\frac{180^\circ(n-2)}{n}\\n=8\end{cases}\implies\delta=135^\circ\therefore\cos\delta=-\cos45^\circ=-\frac{\sqrt{2}}{{2}}[/tex3]
[tex3]\beta=\frac{135^\circ}{2}\therefore\sin\beta=\sqrt{\frac{1-\cos135^\circ}{2}}=\sqrt{\frac{1-(-\cos45^\circ)}{2}}=\frac{\sqrt{2+\sqrt{2}}}{2}[/tex3]
[tex3]\gamma=75^\circ\text{(por Tales)}\therefore\sin\gamma=\cos15^\circ=\sqrt{\frac{1+\cos30^\circ}{2}}=\frac{\sqrt{2+\sqrt{3}}}{2}[/tex3]
Da lei dos senos
[tex3]\frac{b}{\sin\beta}=\frac{a}{\sin\gamma}[/tex3]
[tex3]\frac{a}{\frac{\sqrt{2+\sqrt{3}}}{2}}=\frac{b}{\frac{\sqrt{2+\sqrt{2}}}{2}}\therefore b=a\frac{\sqrt{2+\sqrt{2}}}{\sqrt{2+\sqrt{3}}}[/tex3]
Da lei dos cossenos
[tex3]c^2=a^2+a^2+2a^2\cos\delta[/tex3]
[tex3]c=a\sqrt{(2-2\cos\delta)}=a\sqrt{\[2-2\(-\frac{\sqrt{2}}{{2}}\)\]}=a\sqrt{2+\sqrt{2}}[/tex3]
Novamente da lei dos cossenos
[tex3]d^2=b^2+c^2-2bc\cdot\cos75^\circ[/tex3]
[tex3]d=\sqrt{\(a\frac{\sqrt{2+\sqrt{2}}}{\sqrt{2+\sqrt{3}}}\)^2+\(a\sqrt{2+\sqrt{2}}\)^2-2\(a\frac{\sqrt{2+\sqrt{2}}}{\sqrt{2+\sqrt{3}}}\)\(a\sqrt{2+\sqrt{2}}\)\(-\frac{\sqrt{2}}{2}\)}=a\sqrt{2(2+\sqrt{2})}[/tex3]
Da lei dos senos
[tex3]\frac{d}{\sin\beta}=\frac{a}{\sin\alpha}\therefore\sin\alpha=\frac{a\sin\beta}{d}=\frac{a\sqrt{\frac{2+\sqrt{2}}{2}}}{a\sqrt{2(2+\sqrt{2})}}=\frac{1}{2}[/tex3]