Three radii of Circle S could be denoted as RS1, RS2, and RS3.
Similarly, three radii of Circle U could be denoted as RU1, RU2, and RU3.
The radii of the two circles, Circle S and Circle U, are related because they are congruent circles. This means that not only are their radii the same length, but all corresponding parts of the circles, including the radii, are equal. In other words, RS1 = RU1, RS2 = RU2, and RS3 = RU3, because corresponding radii in congruent circles are equal in length.