a, Ta có \(\widehat{AOD}=\widehat{DOC}=\frac{1}{2}\widehat{AOC}\)
\(\widehat{COE}=\widehat{EOB}=\frac{1}{2}\widehat{COB}\)
\(\Rightarrow\widehat{DOC}+\widehat{COE}=\frac{1}{2}\widehat{AOC}+\frac{1}{2}\widehat{COB}\)
\(\Rightarrow\widehat{DOE}=\frac{1}{2}\widehat{AOB}\Rightarrow\widehat{\frac{DOE}{\widehat{AOB}}=\frac{1}{2}}\)
b,\(0< AOB\le180\)
\(\Rightarrow MAX\left(AOB\right)=180^o\)
\(\Rightarrow MAX\left(DOE\right)=\frac{180}{2}=90\)
Vậy GTLN của DOE là 90 độ
P/s: Max la lớn nhất nha