<P> In mathematics (and more specifically geometry), a semicircle is a one - dimensional locus of points that forms half of a circle . The full arc of a semicircle always measures 180 ° (equivalently, π radians, or a half - turn). It has only one line of symmetry (reflection symmetry). In non-technical usage, the term "semicircle" is sometimes used to refer to a half - disk, which is a two - dimensional geometric shape that also includes the diameter segment from one end of the arc to the other as well as all the interior points . </P> <P> By Thales' theorem, any triangle inscribed in a semicircle with a vertex at each of the endpoints of the semicircle and the third vertex elsewhere on the semicircle is a right triangle, with right angle at the third vertex . </P>

What is the diameter of a semi circle
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