[tex3]OC=OT\implies \angle OTC=\angle TOC=4\theta \implies \angle COT=\pi-8\theta\implies \angle TOA=8\theta\\
(AT)\text{ tangente em $T$ ao círculo }\implies \angle ATO=\frac{\pi}{2}\\
Em \triangle ATO,\,\angle ATO+\angle TOA+\angle OAT=\pi\implies \frac{\pi}{2}+\theta+8\theta=\pi\implies 9\theta=\frac{\pi}{2}\implies\theta=\frac{\pi}{18}=10° [/tex3]...