A regular polygon.
There are always two angles between two radii of the same circle ... starting at one of them and going each direction to the other one. If you define the angle between them as the smaller of the two angles, then it can be anything between 0° and 180°. If you define it as the larger of the two, then it can be anything between 180° and 360°. If you don't care which of the two angles is measured, then it can be anything between 0° and 360°.
sides
yes or no
It is one measure - not the only one - of a "central tendency". It is the same as the "average". To calculate the average, just add all the numbers, and divide the result by the amount of numbers.
yes
yes
NO. All the radii of a circle are of exactly the same length. In fact, that is the definition of the locus of a point describing a circle.
Yes, all of the radii in a single circle are congruent.
All the radii of a circle are of equal length. The radius is the distance from the center of the circle to the out edge. Having equal radii is what defines a circle.
a polygon with all sides the same length and all angles the same measure is called?
triangle
Congruent spheres
concentric circles
72 degrees 72 degrees
A regular polygon.
regular