Additional Information A semi-circle (or semicircle) is simply one-half of circle. It can also be thought of as a sector with an angle of 180 degrees. If the perimeter of the semi-circle is needed, add together the lengths of one-half of the circumference + diameter |
| Where (for brevity) it says 'radius', 'circumference' and so on, it should, more correctly, be something like 'length of radius' or 'size of circumference' etc.
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