c) Ta có: \(\widehat{ABD}\) là góc nội tiếp chắn \(\stackrel\frown{AD}\)
\(\Rightarrow\widehat{ABD}=\dfrac{1}{2}sđ\stackrel\frown{AD}\Rightarrow\stackrel\frown{AD}=2\widehat{ABD}=2.30^0=60^0\)
\(S_{AOD}=\dfrac{\pi R^2n}{360}=\dfrac{\pi R^260}{360}=\dfrac{\pi R^2}{6}\)