Đáp án:
\(sđ\mathop{CD}\limits^{\displaystyle\frown} =20^\circ\)
Giải thích các bước giải:
Ta có:
\(\begin{array}{l}
\quad \widehat{ASB} = \dfrac12\left(sđ\mathop{AB}\limits^{\displaystyle\frown} + sđ\mathop{CD}\limits^{\displaystyle\frown}\right)\\
\Leftrightarrow sđ\mathop{AB}\limits^{\displaystyle\frown} + sđ\mathop{CD}\limits^{\displaystyle\frown} = 2\widehat{ASB} = 2.50^\circ = 100^\circ\\
\Leftrightarrow sđ\mathop{CD}\limits^{\displaystyle\frown} = 100^\circ - sđ\mathop{AB}\limits^{\displaystyle\frown} = 100^\circ - 80^\circ = 20^\circ
\end{array}\)
