[tex3]\angle COD=60°\implies \angle CED=\angle CBD=\frac{1}{2}\angle COD=30°\quad\text{(ângulo no centro)}\\
ABCE \text{ cíclico}\implies \angle CBA+\angle AEC=180°\implies x+(y-30°)=180°\quad\text{(ângulos opostos num quadrilátero cíclico são suplementares)}\\
ABDE \text{ cíclico}\implies \angle DBA+\angle AED=180°\implies y+(x-30°)=180°\\
\therefore 2x+2y=420°, \text{ ou seja }x+y=210°[/tex3]...