For the same reason they chose to measure volume in cubic units
they use protractors to measure circles
With a ruler
They are circles. We measure circles in degrees.
Protractors have to be half- circles because they measure angles less than 360 degrees.
To use a protractor for circles you find the middle of the circle and you then put the dot on the hole then you measure
Because they (IMO) have the simplest area to find, to just square side. Triangles are half of a square Rectangles are uneven. Circles are rounded, and hard to find the area of. Plus, a square has 2 equal dimensions, so think 2D.
Congruent circles, maybe...
Congruent Arcs
Archimedes of Syracuse
A protractor measures the degree of angles and circles.
same circle or congruent circles
Yes; the circle is a special case of an ellipse.