An arc that measures [tex]\(180^\circ\)[/tex] is called a semicircle.
A circle is divided into 360 degrees. Since a semicircle is exactly half of a circle, it measures half of 360 degrees. Therefore:
[tex]\[
\frac{360^\circ}{2} = 180^\circ
\][/tex]
Thus, an arc measuring [tex]\(180^\circ\)[/tex] represents half of the circle, which is defined as a semicircle.
Therefore, the correct answer is:
A. semicircle
