The sum of angles in a circle is 360°. This means that if we calculate the sum of all the arc angles provided for a circle, the result will be 360°.
The image in the question gives two arc angles: 280° and ∠1. Therefore, we have that:
[tex]\angle1+280\degree=360\degree[/tex]
Solving for ∠1, we have:
[tex]\begin{gathered} \angle1=360-280 \\ \angle1=80\degree \end{gathered}[/tex]
The measure of ∠1 is 80°.
