Circles that have congruent radii. Congruent=coinciding at all points when superimposed (http://dictionary.reference.com/browse/congruent)
Are congruent circles.
What the word congruent and circle have in common is that circles have a congruent radii. All of the radii in a single circle is congruent to each other.
They are congruent circles
They are congruent or identical circles
You need only know the radius of each circle to determine that they are congruent. If the radii are identical, the circles are identical. This can also be determined by comparing the diameters (twice the radii), or the circumferences, or the areas of the circles. In all cases, if the parameters are identical, the circles are identical.
Yes. Congruent circles by definition have the same size, and the radius sufficiently describes the size of a circle.
Yes, all of the radii in a single circle are congruent.